by Dale DePriest
The chapter covers the main differences in using the different Garmin units. I focuses on the User interface while presenting an interface philosophy that should permit a user to be able to translate user interface differences between models to the idea behind the interface. The goal is to permit a user to adapt to various models and know how to do a particular function even though a model may be using a different philosophy from the one the user originally learned.
This section covers the philosophy of the Garmin interface and the specifics of most of the handheld units. The emap and etrex are sufficiently different to have their own sections but the overall philosophy is the same. A quick look at the keypad is usually enough to tell the user which of the various interfaces philosophies is used on a particular unit. The emap uses a keypad that is similar to the other handheld units while the etrex uses keys that are all on the sides of the unit. The specifics of the emap and etrex user interfaces are covered in separate sections but the general discussion below applies to them as well.
As with many handheld electronic devices you will be working with your Garmin gps using the keypad. In this case you have a very small keypad not much larger than a watch. Garmin handhelds have ten or twelve buttons that provide the full interface. Actually on later machines the 4 buttons that were the arrow keys have been replaced with a single rocker key that still provide the same 4 directions, while some of the latest units from Garmin uses a miniature joystick that they call a click stick. The keypad on most older units looks like the diagram below:
in out zoom keys only present on some units goto ^ page pwr < > mark called menu on the Garmin III and 76 families quit v enter
The display consists of a series of screens called pages and is very much like a digital watch display. One of the fundamental user interface features is the page key that rotates through the various display pages in the forward direction. (The quit key can be used to rotate through the pages backwards.) The display pages show gps status, positional information about your location, map data, navigation information, routing information, and menu commands to access features that are not available directly from the keypad. As you might expect with so few keys the ones you have are used for multiple things. For example if the gps alerts you to read a message then the page key doubles up as the key you press to read the message. You would then use the quit key to return to the screen you were using before the message appeared.
The quit is how you back out of what you were doing. Thus it will move you the opposite direction from page or it will cancel a command.
Other units have similar functions although the keys may be arranged differently. In particular some units have a "click-stick" which looks small joy stick and performs the same functions as the arrow keys or rocker pad. In addition the stick may be "clicked" by pressing straight down which performs the same function as the enter key.
One of the more interesting features of the Garmin interface is that it emulates the object oriented interface often found with software products that use a mouse. Basically graphic oriented products often let you move the mouse to some object on the screen and just click on it to perform a command or function. Your Garmin emulates this behavior using a select and execute command sequences that combines the use of the arrow keys with the Enter key (or sometimes the menu key on units so equipped) to perform the "click" operation. If you use the arrow keys on any of the pages on you Garmin gps you are likely to find that something on the screen automatically becomes highlighted. As you continue to press the arrow keys you will notice that the object that gets highlighted changes very much like when you move the mouse over objects on the screen. For the Garmin units almost anything on the screen can be an object. For example a title of data can be an object or the data itself can the an object if it can be changed by the user.
If there is only one thing that can be done with the object then selecting it will automatically bring up the screen that lets you work on the object. It there is more than one thing that can be done then the selection will bring up a choice list or menu of commands that you can use. If you have a choice then use the arrow keys to highlight the choice you want and press the enter key to select it. Or you can use the quit key to cancel the command. While an object oriented interface is unusual in a small handheld device the power it brings is appreciated by most people who use it. It provides for less key presses than would be needed by other interface techniques which caters to the power user. The key to understanding this interface is just to use the arrow keys and see what you can select. Depending on what else is happening you may be able to select different things at different times. For example when using the simulation mode available with your unit you may find that you can select additional objects or some objects may be selectable when you first turn the unit on but can no longer be selected after the unit figures things out on its own.
Using the arrow keys is circular. The down arrow keys attempts to move down but if you are already at the bottom then it circles around and you end up at the top. Similarly the up arrow key will also circle. This fact can be very useful if you start at the top and notice the object you want is near the bottom of the screen. Moving up will often get you there quicker than the more traditional way. The left and right keys may do similar things to the up/down keys or they may attempt to highlight items that are logically left or right on the screen. They are also circular but will tend to move up or down as well when the edge of the screen if encountered. Left moves down while right moves up.
While the object interface is powerful there are certain things that are better accomplished using a menu interface. There are two fundamentally different approaches to the menu interface that are used on Garmin receivers. This becomes obvious when you notice that some receivers have a dedicated menu button on the face of the unit while others seemingly don't have any menus at all. A third group of units have no menu button but every screen has a banner at the top with menus always available from the banner. These units are similar to the ones with a menu button in that the interface is very menu oriented.
All of the units in the Garmin III family which includes the G-III, the G-III Pilot, the G-III+, and the 12Map, as well as the 76 family and emap have a menu key where the mark key would normally appear on the other Garmin units. There is a significant difference in the way that you work with these units because of the menu oriented interface but all of the functions are the same. Often the screens and commands are simpler and more straight forward which appeals to some users. However, there are cases where the fundamental object oriented interface is also present. There are two basic menus available to the Garmin units whether explicitly or implicitly defined. There is a local menu associated with each screen that contains commands intended for that screen and there is a global menu that contains all of the machine configuration items and commands that are not specific to one screen. On units with a menu key pressing the menu key once brings up the local menu. Pressing it again without any other keystrokes brings up the global menu. There may also be submenus available either directly from the menu or from a screen that appears as a result of selecting an item from the menu. In some cases the submenu is reached by pressing the menu key but in many cases this is done by providing a tab at the top of the display. These look like file folder tabs and behave similarly. Highlight and select the tab folder to bring it and its contents to the front. Note that there may be more tab folders than can be displayed so you may have to use the left/right arrow keys to scroll sideways to see them. In all cases once the menu appears the arrow keys are used to highlight an item and the enter key is used to select that item or the quit key (esc on the emap) cancels the operation.
The etrex legend and its siblings have a banner on every screen with the screen name on it and two small boxes on the right side. One is a menu that permits selecting from the available pages (including the main menu) and the second is the local menu. Use the "click stick" to highlight the menu (left) button and then click to bring up the local menu. The right button can be used to select a screen providing direct access as a alternative to paging through all of the screens one at a time. A double click on this button will permit toggling between two pages of your choice. Note that the click stick performs the selection movement and may be "clicked" to provide the enter function.
All of the other Garmin handhelds also have a menu interface but it is a bit more subtle. If you press the enter key when there is no object highlighted on the page then you will see a local menu. (Or if there is only one thing that can happen you will execute that command.) Once the menu appears you can highlight the desired command with the arrow keys and select it using the Enter key, or cancel with the quit key, just like you would using the G-III menu system. In addition there is a global menu. Since there is no menu key the global menu appears as just one of the pages in the standard page rotation. So if you hit the page key a few times you will reach the global menu. Submenus are a bit more problematic on units without a menu key. What Garmin has done is to divide the screen into two portions whenever there is a need for a sub-menu. The main screen data plus a menu selection at the bottom of the screen. Most of the design differences in the screen displays between the G-III family and the other units is because of this one difference.
In addition to the local and global menus there is also a banner menu on the map page of some units. Banner menus appear across the top of the screen and contain choices that are specific to that screen. They are easy to recognize because they participate in the highlight mechanism used to select other objects on the screen. Moving the highlighted object using you arrow keys will rotate between screen objects and the banner menu. There will never be a case where nothing is highlighted, which is how you can recognize the banner menu. Selection is done as always using the Enter key. The newest etrex units with the click stick have a banner menu available on all screens. It is used as an alternate way to jump from screen to screen and to access the local page menu. The banner may also display information that is useful to the user.
So far we have discussed the use of the arrow keys, the page key, the enter key, the quit key, and the menu key (if present). It would be possible to design a gps with only this set of keys or even less, however Garmin has singled out some important functions and provided special keys to make them easier and quicker to use. These keys, like the ones we have already discussed, often have multiple uses as well. In some cases the secondary use is reached by pressing the same key a second time in succession like was done with the menu key as described above. In other cases holding the key down for a longer period of time accomplishes the second function.
One of these keys is the power on/off key. This is the red key shown above on the left center of the control panel. It contains a small icon showing a light bulb in its center which points out it secondary use. If you press the power button and the unit is already on the switch will turn on the backlight. On some units pressing it multiple times will toggle through a selection of available lamp brightnesses while other units only have a single lamp function. To conserve battery power the unit has the ability to automatically turn the lamp off after a preset period. If the lamp has turned off by itself then any key depression will light the lamp and you will need to press the key a second time to perform the intended function of the key. To turn the unit off you must hold the button down for several seconds. The 12CX uses this button to bring up the contrast controls as well as for backlighting. The first time it is tapped it brings up the contrast form and the second and third taps control the backlight brightness. The GPS V also uses this button to bring up the contrast controls and lamp controls. The etrex models and emap have placed the power button on the side of the unit.
The goto key provides a quick way to set up the navigation information needed to use your gps as a navigation device. You cannot navigate if you have nowhere to go. The goto key permits defining a destination. Once a destination is selected then the navigation features of you unit can help you to get there. As shipped, the Garmin units include one possible destination, their plant site. I guess they have concluded that everyone would want to visit them so they included this location in the default lists of destinations. Some units now also list their manufacturing site as a choice. As you begin to use your gps I am sure you will find plenty of other destinations as well. Once you press the goto key a list of possible destinations will appear and the unit will take a best guess as to the one you might want. Here is another example of the object oriented approach. If you have a destination highlighted on a list of waypoints or on the map screen then the GOTO command will automatically display this as the default choice. At the bottom of the screen is a submenu of other possible commands. All units have a Cancel GOTO choice and some of the newer units permit you to initiate a TRACKBACK from this menu. (More on trackbacks is in the chapter on routes.) The latest units permit you to jump to the submenu using the right arrow key, otherwise you will have to continuely press the up/down keys until you reach the command. (Remember on the G-III these submenu items are on the folder tabs.)
In addition to the primary goto function there is a special goto function that is reached by pressing the GOTO key twice in a row. This automatically create a special waypoint called MOB at your current location. (Not available on the G-III Pilot or units with no goto key but is available on the 76 family using the nav key.) Pressing enter at this point will cause the navigation screens to begin to show navigation information to the MOB waypoint. MOB stands for Man OverBoard and is intended to help a boat return quickly to the spot where a person fell out of the boat. Most people find other uses for this as well.
The G-III pilot uses the secondary function of the goto key to perform a find nearest command by holding the goto key down for a second or more. This function paved the way for the dedicated find key that appears on the emap, newer etrex units and the gps V.
The newer units do not support a goto function key but use an object oriented approach of selecting the waypoint and then selecting goto. On the 76 and Map76 this has resulted in the goto key being replaced by a nav key which is used to toggle navigation on/off but the secondary mob function on this key is still present if you hold the key down.
The mark key is used to mark (save) your current location. On units with no mark key the ENTER key can be held down for a second or so and the mark screen will appear. Once the mark screen appears you can save the current location as a new waypoint. Waypoints are simply saved locations. They can be used as destinations or intermediate destinations on a route. They will be shown on the map screen when you get close to one of them. Waypoints are quite useful in helping you orient yourself to your present location or when navigating.
On the G-II family, the G-III family, and the GPS V the page key also has a secondary function. These units are capable of displaying their screens either vertically in portrait mode or horizontally in landscape mode. Hold down the PAGE key for a short period will cause the screen to switch modes. (You can also do this from the global menu but this key is a lot easier.)
The etrex has limited keys and uses the page key as a cancel key as well. If you are inside the menu system the page key is defined as cancel while its page function only really works if nothing else is selected. On any unit the page key may be the best way to bail out of a bunch of menus if you have moved deep within the menuing system.
Some units also have two extra keys that are dedicated to zooming. These are used on the map page to change the scale of the map. They may also be used on the road navigation page to change the scale of the displayed road which, in effect, changes the scale of the cross track error. This function is implemented on those units have a cross track error display as part of the compass the compass page. On the etrex the zoom keys are on the side of the unit. <4>Find Key
The find key characterizes most of the new third generation units. It indicates addition functionality is present that expands the waypoint idea to include other objects that can be 'found' in the database.
The find key was new with the introduction of the emap handheld unit and copies the Street Pilot functionality. (The Street Pilot is Garmin's name for their larger automotive units.) It becomes important when you need to look up, or find, information on the map and demonstrates the focus of that product on mapping and locating information. In addition Pressing and holding the find key while navigation is active will jump to the goto waypoint screen or route screen as appropriate showing the active route. This provides a quick way to see the current destination since this is not displayed on the main screen and it provides more navigation data. All of the newest units include a find key.
The find key brings up a menu that permits finding any of the objects in the database of the unit. Which objects are available are determined by what maps may be loaded in the unit. Possible objects include waypoints (always present), cities, freeway exits, poi's (points of interest), street addresses, and intersections. Many objects can be listed by their distance from your location or in alphabetical order. Some units will even let you set up a favorites list. The GPS V offers a list of recently selected places.
Generally the function keys can be depressed at anytime and will
perform the function on the key. For example you might be doing
something in the menus and suddenly find the need to mark a location.
The operating system supplied as part of your unit is designed to
permit this kind of interaction.
The basic etrex only has 5 keys and these are located on the sides of the unit where they are expected to be operated while the gps is being carried in the palm of your hand. These are the power on/off key, the page key, an up key, a down key, and the enter key. These are shown in the diagram below:
Up < > Page/Cancel Down < Enter/mark < > Power/lamp
The page key is present to move from screen to screen just as in the other handheld units. It also doubles as the cancel key whenever you are within some submenu function. The power on/off key doubles as the lamp key just as it does on the other units. The enter key also retains much of its same meaning and even doubles as the mark function by holding it down for a long period just as it does on the Garmin III family and emap. It can be used to bring up a local menu on the map or pointer screen.
A unique feature of this unit is the lack of a keypad or arrow keys. Instead there is the much simpler to manipulate up/down key set. These keys have dedicated functions within the scope of the screen that is currently being displayed. These functions are:
There are very few dedicated keys on this unit. The functions performed by dedicated keys on other units are reached by accessing the main menu on this unit. The goto function is provided using an object oriented approach of selecting the object (waypoint) first.
These are new models from Garmin that share a case design with the standard etrex but are characterized with a new keypad area called a "Click Stick". This is a small joystick located above the screen display. It performs the standard functions of the rocker key and can be depressed straight down as well to do the enter function. With these functions handed by the "click stick" the 5 keys on the sides can be defined for other things. This leads to the following key arrangement:
Zoom in < > Page/Cancel Zoom out < Find < > Power/lamp
The zoom functions are used to control the contrast on the status
page and the find key is used to provide a new direct function for
searching the database. This arrangement on the sides of the unit
lends itself to handheld use but it a little cumbersome for use
mounted in a car.
The emap keypad arrangement looks similar to the keypad on other Garmin units except that it is below the screen area and, upon close inspection, there seems to be some keys missing. Indeed there are, the power and backlight keys are on the side of the unit instead of the top and they are separate keys. The backlight keys doubles as the key used to bring up the contrast menu by holding it down for a second or so. The keypad arrangement looks like this figure:
in ^ out dedicated zoom keys find < > menu esc v enter/mark
The key names on the keypad provide a clue that this unit is different from the other Garmin products. It focuses on using a map display and is designed from the ground up to be a mapping receiver that uses the functions of a gps to provide information for the map display. When the unit is turned on you must acknowledge the warning screen as with other mapping receivers and you are then shown the map screen. There is no page key or any method to rotate through other screens. Instead the navigation data that you may need is available from the main global menu (reached by pressing the menu key twice). The menu and enter/mark keys are in their traditional locations while the zoom keys replace the goto and page keys. The goto function key is not used on the emap being replaced with an objected oriented approach. The esc key performs the function of backing out of any menu item (escaping) and if pressed and held down for a second it will totally back out from all menus, screens, and functions and return to the map screen. The find usage was covered above in the general section.
To enter data into the gps you must first highlight the field containing the data you wish to change. The full field will be highlighted; you then push the enter key. The highlighting will change to just a character to indicate selection. Now you will use the arrow keys to actually change the data. There are two kinds of fields, one permits changing from a fixed collection of values while the second permits you to enter the data free form. With the first form you use the up and down arrow keys to move through the choices until you arrive at the one you wish and then hit enter to select that choice. (Enter quit to cancel). For the second entry type you would use the up and down arrow keys to select the first character for the entry and then use the right arrow key to move to the second character and continue until you are finished. The enter key completes the operation or use quit (esc on emap, page on etrex) to cancel.
Since the basic etrex has no left or right arrow keys it uses a slightly modified form of data entry. When you hit enter to select the field to edit you actually only select one character. The up/down keys are used to choose the new character from a list (menu). The enter key is then tapped to confirm the selection. If you hit enter again without using the up/down keys you will select the next character for modification.
| The etrex legend and its
siblings use a menu system to provide for data entry as does the gps
V. Once a selection is made a table of characters appears on the
screen as shown on the left. All four directions on the "click stick"
can be used highlight the desired character and then a click will
select it. The next character can then be entered. The menu selection
also includes certain commands near the center of the display for easy
access. Any character or command that is not legal in this context is
The commands in the table include the ability to move the data entry cursor left and right (arrow functions) as well as a backspace and Space function as well shift and OK entries. Note that, for waypoint entry, as shown in the example, there are no shifted characters so the shift function is grayed out. If you use the left arrow function and move past the left most character the field will be completely cleared as is the case for other forms of data entry used on other Garmin units. If this was a mistake you can use the right arrow key to get the old data back unless you have started to enter replacement data. To cancel the entry press the page key as usual. In a few cases the menu may show a +/- menu item that allows you to move through a predefined list, such as the months of the year.
No matter which model you own there are some special features to help ensure success with data entry. You will not be given a choice if its not legal. For example waypoints cannot have a space in their name (except on the emap, newer etrex units, 76 line, and GPS V). The space character is visually shown as an _ (underscore) and thus it will not appear in the choice list for the field on units that don't permit embedded spaces unless you are on the last character and wish to erase it by entering a space. If the field only wants numeric data then the rotation through the characters will only present numeric data. The left and right arrow keys can be used to backup or move to the next character. If you back past the beginning of the field the entire field will be erased (set to all underscores or 0). This can be very useful and can be used at the very beginning of entry to zero out or clear a field. You should continue to change the entries until all of the characters have been entered. The right arrow key will skip over any data that you cannot change. Only hit the enter key after all of the data has been changed. The quit key (page on the etrex and esc on the emap) can be used to cancel the character entry.
In summary here are five basic types of interfaces in your Garmin gps.
Data entry is accomplished using the keypad and selecting the characters by scrolling or menu selection. The enter key is used to confirm the data entry or the individual selected character on the etrex.
In the rest of this manual you will be assumed to know how to use the
interface and the various differences between the models. For example
if the subject is about marking a location you should know that you
can use the mark key on some units but may have to hold down the enter
key on some others. Equally you should know how to access the global
or local menu on your particular unit. If there are unique techniques
that are model specific then they will be covered as needed.
The Display and System Setup
For the most part the display interface is fixed by the design of the
unit. However on some of the newer units there are plenty of things you can
customize to meet you needs. Some units are designed for use over the
whole world and even permit customizing the language that the messages
are displayed in. All Garmin units will work worldwide but the ones
with builtin databases may be optimized for one area or another. For
example the city databases may show more and smaller cities in one
area and the maps may favor a given part of the world.
The screen display customization for each screen will be covered in the chapter on display screens and navigation customization will be covered in the sections on navigation and coordinate systems but there is also customization that is just for the system itself. This customization is reached from the main menu under the title SYSTEM or SETUP and then SYSTEM. Once there you will see some information about the date and time. The date is set automatically and the time is also set automatically by the gps system. You can change the display of the time by changing the entry marked OFFSET. This is a numeric field where negative numbers represent time west of UTC and positive numbers are east. PST in california should be set to -8:00 hours and during Day Light Savings time it should be set to -7:00 hours. You can also decide how time is to be displayed: in 12 hour am/pm mode or 24 hour military time. On the etrex and emap you can also set automatic daylight savings time support and set the time zone using more traditional pneumonics in some cases.
Screen Contrast can also be set here or in the status screen (except for the 12CX, etrex, and emap) and there is a setting for the backlight. Turning on the backlight causes the unit to consume more current and thus the battery life suffers. For this reason the lamp will automatically turn off after a fixed delay. You can customize the length of this delay on this menu. Setting zero delay causes the lamp turn-off delay to be disabled. Most units also disable the delay automatically when you are using external power to operate the unit.
You can also set the mode of operation from this screen. These include normal, battery-save and simulation mode.
On newer 12 channel units the battery save mode, also known as power save, will also limit the number of satellites being tracked. This is done by changing the mask angle to limit the unit from attempting to track satellites that are close to the horizon. (Older multiplex units do this in all modes.) Solutions depending on these low lying satellites are generally less accurate due to tropospheric delays. With a clear sky view battery-save mode can offer a significantly longer battery life with little degradation in service. In forest regions the accuracy suffers much more, particularly when traveling in vehicles. Waiting 5 seconds (3 seconds in older units) between fixes can cause a loss of lock in some cases and contribute to even longer excursions offtrack than a momentary loss in normal mode. If you are experiencing long straight tracks with sharp bends when traveling on a winding road the battery-save mode should be discontinued to maintain best accuracy.
Another setting that is user specified on some units is the Language setting under the SETUP menu selection. Here the user can specify which language they prefer to use. The G-12 family and the new etrex family supports this feature and permits choices that include: English, Danish, French, German, Italian, Spanish, Swedish, Portuguese, and Norwegian.
The G-II family, the G-III family, and teh GPS V, have a portrait and landscape mode option that can switch the display to optimize for use while being handheld or when placed on the dashboard of you car. This can be switched by holding the page key down for a few seconds or setting the preferred direction in the System Setup menu. Note that, in particular, the G-III family has independent customization settings for the portrait screen and the landscape screen. You can move information around for the two screen displays or you can even have different information on the two displays.
The GPS V has a battery selection option and WAAS selection on this screen.
All Garmin units have alarms that alert you to any unusual events. The alarms can be visual or audible. While all units can provide visual alarms only certain units can sound an audible alarm. The visual alarm is sounded two ways, a box appears alerting you of the presence of a message, and at night when the lamp is in use it will automatically light for alarms after its normal time out. Generally you can acknowledge an alarm by using the PAGE key to read the message or if you ignore it the alarm will reset if the condition that caused it goes away. On units with an audible alarm you can customize the tone usage on the setup page. You can set it to beep on key presses, only messages, or off.
On most older units part of the alarms are configurable from the ALARM entry on the setup page. Alarms associated with arrival at a waypoint can be turned off, on with a specified distance, or automatic. Automatic alarms occur when you are one minute away from getting to the waypoint at your present speed and direction. The etrex units have set the alarm to 15 seconds while the emap and gps V automatically increases the alarm time based on the speed as shown in the table to the right.
There may also be a configurable CDI, or off course alarm that can be turned on or off. (CDI is explained in the navigation chapter.) Some units designed for marine use also have an anchor alarm that can be configured on or off as well has how far you are going to permit the boat to drift. There can also be proximity alarms which are triggered by being within an individually configurable distance of a waypoint. The Garmin III family also has a visual alarm clock that can be turned on or off.
Units supporting WAAS will have an enable/disable setting on this menu. WAAS is covered in the miscellaneous chapter. Selecting enable turns WAAS on. You should be in normal mode for this to work properly as WAAS needs to receive updates more often than permitted in battery save mode.
On many units all of system setup in on a single menu pick
called setup. You then tab across to get the setup settings you need
on mapping units or pick from a submenu on other units. Most of the system
settings are described above but other settings are described in other
chapters as needed. The time setting includes a display of the current
time and is the only place that you can see the exact seconds for the
time on the emap.
Any standard AA batteries can be used in Garmin receivers. Some units have the ability to set the battery type in SETUP so that the battery gauge properly reflects the state of charge for the battery. For example in the G-12 family of units a fully charge set of NiCad batteries will only show 3/4 charge on the meter while the G-III family setup entry to support NiCad batteries would show full charge. This setting generally only effects the meter and the low battery alarm which is set to approximately 4.0 volts (1.9 volts on the etrex, 76 series, and emap) will work fine for either battery type although you won't get much warning for rechargeables. On some units the low battery warning is modified as well to give longer time. On my emap the momentary current drain of the audible alarm will shut the unit down at the low battery warning so there is no warning at all unless I turn the alarm sound off. There is more information on batteries in the "Getting Started" chapter.
All of the gps units with the exception of the etrex, emap, gps V, and 76 family also contain a backup battery. (These 3 Volt units and the gps V do not need a backup battery since the data in these units is stored in non-volatile memory.) The internal clock on these units is run from a storage capacitor and will only last a week or so without batteries but this is not critical. A backup battery preserves critical user data when the normal batteries are removed from the unit. The backup battery has a life of about 3 months but it is rechargeable from the main batteries. If this battery runs down you will lose all user data and the almanac which will greatly increase the time to obtain a fix. You will need to recharge it by leaving a set of regular batteries in the unit for about 24 hours with the unit off or on external power for a couple of days. It is best to keep a set of alkaline batteries installed at all times, even when you are not using the unit, to ensure that the backup battery remains charged. On the etrex and emap it is probably a good idea to remove the batteries if you are not planning to use them for a long period. Expect a longer lockup time the first time you reuse these units after storage. The almanac data will probably be out of date and the internal clock will likely be wrong, particularly if the batteries were removed from an etrex, 76, V, or emap.
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