Chevrolet, Buick, and Cadillac odometers cannot be rolled back – at least not without it being apparent to any used-car dealer. Since 1969 General Motors can have had two thin white plastic flags, normally held out of view by a seal, in the odometer case. Tampering with the odometer breaks the seal, and the flags drop into view. They appear as two telltale vertical lines on either side of the thousands’ digit – for example, 3/1/820.1.
GM dealers seem to have benefited most from the device. Few customers know what to look for. Absence of the lines is no guarantee of accurate milage. Dealers can buy replacement seals (from independent manufacturers, not GM) to conceal the lines on a doctored car.
From the book Big Secrets by William Poundstone
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