Garmin GPS III Plus Owner's Manual - Page 88

REFERENCE Setup Menu: Units Select nautical, statute or metric units of measure from the 'Units' settings. The 'User Mag' option allows you to define the magnetic variation for your area. 'Auto Mag Var' is the preferred setting in most cases. 78 Units Settings Distance & Speed lets you select the desired units of measure for distance and speed readouts in 'Nautical', 'Statute' or 'Metric' terms. Heading lets you select the reference used in calculating heading information. You can select from 'Auto Mag Var', 'True', 'Grid' and 'User Mag Var'. 'Auto Mag Var' provides magnetic north heading references which are automatically determined from your current position. 'True' provides headings based upon a true north reference. 'Grid' provides headings based on a grid north reference (and is used in conjunction with the grid position formats described on page 82). 'User Mag Var' allows you to specify the magnetic variation at your current position and provides magnetic north heading references based upon the variation you enter. Altitude lets you select altitude readouts in 'Feet' or 'Meters'. To select a units setting: 1. Highlight the desired field and press ENTER to display the available options. 2. Select the desired option and press ENTER. 3. If 'User Mag Var' is selected in the 'Heading' field, highlight the heading reference field (immediately to the right) and press ENTER. Enter the magnetic variation at your current position using the rocker keypad and press ENTER. I WARNING: If 'User Mag Var' is selected, you must periodically update the magnetic variation as your position changes. Using this setting, the GPS III+ will not automatically calculate and update the magnetic variation at your present position. Failure to update this setting may result in substantial differences between the information displayed on your GPS III+ and external references, such as a magnetic compass.