What does this knob do?

[cab13367]

The adjustment knob below is located under/behind the dash. Anyone know what it does? I suspect it has something to do with calibrating the Perfect Pass but I don't remember reading anything about it in the PP documentation.

Thanks,

Al

http://i250.photobucket.com/albums/gg276/cab13367/IMG_0962.jpg

[TL7]

If I'm not mistaken that's to calibrate the speedo. I'm sure someone will correct me if I'm wrong.

[csmsk]

Cab is right. I use them to match my speedos to my GPS.

[csmsk]

Sorry, TL7 gets the credit.

[cab13367]

Thanks guys.