[. . . ] IMPORTANT COMPASS INFORMATION Why do I have to Calibrate the Compass?The compass in your ESD-9870 must be calibrated before you use it to give accurate directions. [. . . ] Press and release the Set/City button and you will hear "Set Compass"(or 1 beep in Tone Mode) and see Drive in 2 circles. It does not matter what direction your vehicle is pointing when you start the circles, which direction you go to make the circles, and it does not have to be exactly 2 circles. Four 3-point turns, 2 small squares, or any 2 complete loops will work as well as 2 circles. It does not matter what size the circles are, if your speed is constant, or how fast you make the circles (but less than 2 minutes). Please be careful when making the circles and watch for other traffic!Press the Set/City button again and you will hear "Compass Set" (or 3 beeps in Tone Mode) and see Compass Set!In the event that the compass is not giving accurate directions after this calibration, please try the calibration again, but in a different location. Magnetic fields at the location you are doing the circles may cause problems with calibration. The compass electronics holds the information about the magnetic fields made by your vehicle. However, for best results, you should mount the ESD-9870 in exactly the same location every time you use it. When you remove the ESD-9870 from your windshield it is best to leave the mounting bracket on your windshield so that when you replace the ESD-9870 it is mounted, again, in exactly the same place. If you decide to re-locate your ESD-9870 to a different place (either on the windshield or on the dash), it is best to calibrate the compass again. [. . . ] Your compass will work again correctly as soon as you get away from these locations. There is no need to calibrate your compass again after this. Part No. : 480-073-P [. . . ]