From GpsWiki
Compass FAQ
How do I get to the Compass page?
If you have the Compass page enabled in Page Order (default from factory), either press the PAGE button or the QUIT button to scroll through the pages until you get to the Compass page. If the Compass page has been disabled in Page Order, then press the MENU button, use the UP/DOWN rocker pad to select Compass, then press ENTER.
What kind of compass does the PN-40 have?
The unit has a three-axis electronic compass.
What does three-axis mean?
It means that you can use the compass with the unit in any position. A GPSr with a two-axis compass must be held flat in order for the compass to function. It also means that the calibration "dance" is a little more complicated.
Why do I need a built-in compass?
You don't need one, but it is nice to have in some situations. There are lot of features which depend on knowing your direction of travel. For example, if you are navigating (a direct route) to a waypoint, the "pointer" needs direction of travel. Similarly, if you have the unit set to Heading Up, the map orientation depends on your direction of travel. Like all GPSrs, the unit can use satellite information to determine direction of travel -- but only when you are moving. When the compass is enabled, the unit can use it to determine the direction you are facing -- even when you are standing still. This helps with location awareness, and can be useful when you're trying to pick a reasonable route. Not to mention when geocaching.
Does the unit ignore satellite direction of travel when the compass is on?
Only when you are moving slowly. According to the PN-40 manual, switchover occurs at 0.5 mph. According to a forum post by DeLorme staff, switchover occurs at 1.5 mph. Either way, above that speed, the unit uses satellite information exclusively.
Can I change the speed at which switchover occurs?
No.
Does the compass use magnetic north or true north?
The PN-40 can be setup to use either magnetic or true north. When magnetic is choosen, a 'M' is displayed in the info field. When true north has been selected, a 'T' will be displayed. See Device Setup-Units-Bearing for more information.
Does "electronic" mean that the compass works in close proximity to metal?
No. The compass still depends on the earth's magnetic field. It will not work near large metal objects (such as your car), or in close proximity to high-voltage power lines. The unit will, however, warn you when there is interference from the environment. On some screens, "Poor Accuracy" will appear in the lower right corner. A red exclamation point also appears in the bearing info field.
Does the compass work reliably in a vehicle?
Generally not. The typical symptom is that the direction of travel changes abruptly when you stop moving, such as when you stop at a traffic light.
How do I turn the compass on and off?
Menu->Device Setup->Compass & Altimeter. Scroll to Enable Electronic Compass. Press Enter to check or uncheck the box.
How often do I need to calibrate the compass?
The manual says to calibrate whenever you change battery types. The consensus seems to be that it is safer to calibrate whenever you change batteries. Calibrate when you see the "Poor Accuracy" warning in situations where there is no apparent reason for it. Calibrate whenever you think the compass readings are unreasonable. In short, calibrate early and often!
How do I calibrate the compass?
Menu->Device Setup->Compass & Altimeter. Scroll to Calibrate and press Enter. Scroll to Calibrate Compass and press Enter. Or, from the satellite screen or compass screen, Menu->Calibrate->Calibrate Compass. Follow the directions on the screen. You will get the best results if you perform the motions smoothly and at a moderate speed. Be sure to keep the unit in the indicated plane, and do not exceed 180 degree rotation in the plane. It is not unusual for calibration to fail occasionally. Just try again.
No matter what I do, calibration fails. What now?
It may be that the accelerometer needs to be calibrated. The PN-40 has an accelerometer which is used during compass calibration. If compass calibration fails repeatedly, and especially if it fails before you can even begin the "dance", see these instructions to calibrate the accelerometer. One user reported that even this did not help, but pulling the batteries for five minutes made the difference.
Why does the orientation of my map change when I stop traveling?
When the Map Page is set to Heading Up, the direction of travel is used to determine the orientation of the map. As long as you are moving at least 1.0mph, the PN-40 uses the satellite information to determine your direction of travel. As the satellite information is fairly accurate at speeds of 1.0 mph or faster, the orientation of the map will be displayed correctly. When you stop moving (speed < 1.0 mph), the electronic compass is used to determine your direction of travel. While inside of a car (or if you haven't calibrated the compass), the electronic compass value can be way off. This then causes the orientation of the map page to change when you stop. Not much can be done while inside of a metal vechicle, but if this occurs while hiking, then you should calibrate the compass.
