Good original 1981 Chevrolet Dealer Computer Command Control System Service Manual System. This Shop Manual Supplement was meant to be used with the 1981 Service/Shop Manual and has the updated information and troubleshooting for the Computer Control Systems on Chevy Models.  It contains information, specifications, illustrations, diagrams and procedures. These are what the Dealerships used to repair your car. Very informative and rare item that will make a useful tool for the Chevy Owner.