Most Ford and GM models and a few Chrysler products have a Data Retrieval System or more commonly called " black box ". This ingenious invention of big brother measures wheel speed,rpm,braking,and several other things 5 seconds before a crash.They were supposely designed to aid the mechanic in diagnosing vehicle related problems but its info is showing up in court a lot.Are they correct ? How often are they checked or calibrated ? Next time you get a tune up ask the mechanic if he calibrated your DRS and see what he says,it had better be right because it can be used for or against the driver.Uncle Sam wants these units in ALL vehicles by 2008.Will they be put in tractors ? Or have they already started ?