RE: compass calibration
You pressed what button? The zone setting is an adjustment for magnetic deviation from true north. The '93 service manual says:
True North Adjustment
The vehicle has been demagnetized and the compass has been calibrated by the manufacturer. However, the True North Adjustment is not done by the manufacturer. Vehicle location in the country will determine how accurate the compass is without performing the True North Adjustment. When the vehicle is received from the manufacturer or whenever a vehicle operator claims that the compass is inaccurate, perform the True North Adjustment Procedure. The compass True North Adjustment is set as follows:
1. Press and hold the COMPASS button, then press the RESET button. The message center will display the following:
E/M > ZONE
RSET > CAL
COMPAS > N
2. Press the ENGLISH/METRIC button to enter the Set Zone mode, as indicated by the top line of the display (E/M > ZONE). The display will now show:
RESET TO
SET ZONE 8
3. Determine which zone of the continent you are in by using the accompanying zone map.
4. Press the RESET button until the appropriate zone number appears on the display. (The zone number will increment once each time the RESET button is pressed. Once the number reaches 15, it will change back to 1).
5. Press the ENGLISH/METRIC button to complete the zone setting. (The Set Zone Mode can be aborted by pressing any button other than RESET and ENGLISH/METRIC). The message center will now display:
SETTING
COMPASS
for a few seconds, and then it will return to the normal compass heading mode. The zone setting procedure (True North Adjustment) is now complete.
California is in Zone 4. To calibrate the compass:
Calibration Adjustment
The compass was calibrated at the factory and under normal driving conditions will not need to be re-calibrated. The compass is designed to re-calibrate itself if changes in vehicle magnetics occur. In order to re-calibrate itself, the compass requires the vehicle to be driven in full 360 degree circles. Occasionally, the vehicle magnetics will change enough to prevent the compass from correcting itself. If the True North (Variation) Adjustment outlined above does not correct an inaccurate compass, the compass should be calibrated. If a compass transducer unit is newly installed in a vehicle, the calibration procedure must be performed.
To calibrate the compass, perform the following procedure:
1. Find an open area free from steel structures and high voltage lines.
2. Press and hold the COMPASS button, then press the RESET button. The message center will display the following:
E/M > ZONE
RSET > CAL
COMPAS > N
3. Press the RESET button to enter the Calibration mode, as indicated by the middle line of the display (RSET > CAL). The display will now show:
CIRCLE
SLOWLY
TO CAL
4. Slowly drive the vehicle (less than 3 mph/5 km/h) in a circle until the message center displays a direction instead of the CIRCLE SLOWLY TO CAL message. If after three complete circles the display still shows "CIRCLE SLOWLY TO CAL", perform the «Vehicle Demagnetizing Procedure» .
5. Perform the «True North Adjustment Procedure.» Calibration is now complete.
I have only once calibrated my compass and I never knew about the True North Adjustment. I hope this helps.