This handy device makes it possible to change ignition timing on your Model A while the engine is running. This procedure maintains the original full 40 degree range of advance that is necessary for proper engine performance. Using this device along with the Precision Timing Kit, your Model A timing procedure will be as user friendly as the modern cars and as accurate, too. Modification to the spark control rod and the distributor cap is required. Instructions for use are included. This is a genuie Nu-Rex product.