Mirror Compass Calibration

Has anyone else here ever checked the calibration of their mirror-compass?

When I bought my car, a 1-owner California car, the mirror was still set to Detroit's
longitude 8 years after it was first sold! So much for "dealer prep"...

Yes, I was Anal enough to read my owner's manual after buying the car and the PO had it set to Detroit longitude still.
having worked at a dealership for a while and reading the new Car Prep Checklist, Setting the Compass was not on any prep sheet.
So the mechanic's responsible would not know to do it and boneheads like me that were responsible reviewing said checklist's didn't have a clue either.

Rickw wrote:

Yes, I was Anal enough to read my owner's manual after buying the car and the PO had it set to Detroit longitude still.

Rickw wrote:

Yes, I was Anal enough to read my owner's manual after buying the car and the PO had it set to Detroit longitude still.
having worked at a dealership for a while and reading the new Car Prep Checklist, Setting the Compass was not on any prep sheet.
So the mechanic's responsible would not know to do it and boneheads like me that were responsible reviewing said checklist's didn't have a clue either.

I did too, but I thought it might have reset to Detroit if the battery had been disconnected - so I just changed the declination setting and recalibrated.

Funny thing - I wish they could have made it easier to reset/recalibrate because when I go east to NYC or west to Ohio the declination settings become wrong. The problem then is that visual cues (the direction of shadows for instance) then sometimes don't match what the compass is telling me. I guess you could say it's noticeable but not *that* big a deal once your remember what's going on.

Albertj

Not only do you have to set the 'variation' depending on where you live, but if you want it to be accurate you also need to put it into 'calibration' mode and drive around in some slow consistent circles. One of the first things I did when I got my Riv.

(I calibrate marine compasses for a side-living)

I calibrated mine once, but didn't notice much difference. Since that time, I've drained my battery completely a couple times, and disconnected the mirror for a week, and it still reads perfect.

Quote :

The problem then is that visual cues (the direction of shadows for instance) then sometimes don't match what the compass is telling me. I guess you could say it's noticeable but not *that* big a deal once your remember what's going on.

I've noticed this as well, but I don't think the compass is wrong. The sun doesn't always project accurate shadows, because throughout the year it moves on different paths across the sky. It also varies depending on N/S location:

good points Aaron...

Except, in the Northern Hemisphere (where we are) doesn't the sun's apparent arc run southerly? In your drawing it runs northerly.

If so the angles in your drawing are about right for the seasons in North America but the compass headings should be flipped N/S. Looks like your drawing was done for maybe Chile or Australia. Or southern Africa...

That is, the reason the equatorial regions are tropical is they get more hours of and more consistent sun. Sun shines, in general, on the southern exposures of buildings in the northern hemisphere, and on the northern exposures of buildings in the southern hemisphere... your drawing shows sun on northern exposures.

Comments?

Albertj

albertj wrote:

If so the angles in your drawing are about right for the seasons in North America but the compass headings should be flipped N/S. Looks like your drawing was done for maybe Chile or Australia. Or southern Africa...

That is, the reason the equatorial regions are tropical is they get more hours of and more consistent sun. Sun shines, in general, on the southern exposures of buildings in the northern hemisphere, and on the northern exposures of buildings in the southern hemisphere... your drawing shows sun on northern exposures.

Comments?

Albertj

You are correct Sir,
Having lived in both Regions for a time, I can confirm.
But, you know AA was just trying to make a point without being astronomically correct.

Yes, the shadow angles should be reversed, but the diagram would be correct for someone in the southern hemisphere. Either way, you won't get a perfect overhead path of the sun unless you live somewhere ~12º north or south latitude, like in northern parts of Australia. There the shadows would point almost directly east or west for much of the year.

I just purchased one that was out of a 99+ Intrigue. It's supposed to be a plug and play unit. The map lights and auto dim work perfectly fine but... The compass only reads NW most of the time. Sometimes it will switch to W or N. I know it's wrong because I was driving on I-91 S and it read NW.

Is this just a bad unit or is there a way to calibrate it?

I got this..

Let me know if you need help. I ran mine through the calibration (it's in the owners manual) and not that it matters but I also calibrate boat compasses on the side.

DEMonte1997 wrote:

I just purchased one that was out of a 99+ Intrigue. It's supposed to be a plug and play unit. The map lights and auto dim work perfectly fine but... The compass only reads NW most of the time. Sometimes it will switch to W or N. I know it's wrong because I was driving on I-91 S and it read NW.

Is this just a bad unit or is there a way to calibrate it?

Should be able to follow the directions in the Riv's owners' manual to reset the compass declination. Declination mis-set is enough to mess up your reasings in the way you describe.

Else - could be a bad unit, although I've *never* heard of one going bad.

Albertj

When i wired up one of those to work in my 96 i had to calibrate it.
manula says to drive in a slow (<5mph) tight circle 2-3 times to calibrate the compass.

Mine is from an Olds Alero and it has extra lights on the bottom that point perfectly in the laps of the driver/passenger.
defiantly worth the afternoon of running a few wires around.

Mine might be bad which is odd... To reset, I had to hold down both map lights. After 10 seconds, the screen changes and displays an "8". That stays for another 10 seconds. I tried the driving in circles going slowly as described here. Did it twice and it didn't change. The mirror almost constantly reads "NW". What really worries me is that this compass only reads "NW" and "N". WTF? Guess the compass unit itself is ruined or something.. I might have to alert the seller to this and hope they are good with customer service.

Rick you likely have a bad compass, I just got mine working, took 2 tries from the junk yard to get one that worked, the 1st one did just like yours.

For those with no owners manual I found this just yesterday.The zones are in there.
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http://www.extendedgmwarranty.com/owners-manual/buick/1999-Buick-Riviera.pdf

Ed,

That's a really helpful link and I found it interesting how it describes the different zones. I guess that's why mine reads "8" when I try to calibrate it. Is it possible that I need to change that to "12" and then it might figure out the other different directions? Maybe I'm hoping for something that's not possible.. hahaha

Aint going to hurt to try but while trying different numbers in mine it just messed with calibration, all directions were still working though.

that is exactly what mine did before i did the circle calibration. Mine eventually just read "C" which is when i did the 3 circles.

when you do the circle calibration try to use a relatively open area like the outskirts of a shopping mall parking lot on a Sunday afternoon, or other large open area.

Albertj

I'm going to try that again. When I did it the first time, the parking lot wasn't exactly empty and if memory serves the instructions said to stay away from metal objects as that may screw up the calibration. The neighboring cars may have been detrimental.

DEMonte1997 wrote:

I'm going to try that again. When I did it the first time, the parking lot wasn't exactly empty and if memory serves the instructions said to stay away from metal objects as that may screw up the calibration. The neighboring cars may have been detrimental.

And you need to keep going in circles until it changes to "C" on the display. It may take 3 or more circles. Find a reaaaly roomy parking lot where you can get away from everything.

If I ever get pulled over for doing donuts in a public lot, I'm going to tell the officer "I was setting my compass, sir."

deekster_caddy wrote:

DEMonte1997 wrote:

I'm going to try that again. When I did it the first time, the parking lot wasn't exactly empty and if memory serves the instructions said to stay away from metal objects as that may screw up the calibration. The neighboring cars may have been detrimental.

And you need to keep going in circles until it changes to "C" on the display. It may take 3 or more circles. Find a reaaaly roomy parking lot where you can get away from everything.

Good call Derek. I'll try the local mall. There really isn't anything in that lot except for a few light posts or maybe the abandoned movie theater.

LOL @ Aaron!

Take a lat-G meter with you and get a skid pad reading!