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Click on image for the lowdown. 
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Apr 26th, 2026 | | AD Chevy Trucks  Over 6,000 pictures Brad Allen has an awesome collection of Chevrolet factory pictures that he has set up from film strips. Check them out!
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| | | | Joined: Sep 2001 Posts: 29,269 Bubba - Curmudgeon | | Bubba - Curmudgeon Joined: Sep 2001 Posts: 29,269 |
I think it was originally used to allow easy advance or retard adjustments (and return to "mark") due to varying grades of gasoline and or for travelling at different altitudes?
Tim
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