This sale is for a new old stock vintage 1944 AC mechanical tachograph.     This tachograph fits early 1940's GMC trucks.  Note that the measurement is in hundreds, not thousands.   0-10  or 0-1000 rpm.     The information on this item is: Made in USA. -  AC div. G.M.C.  -1536140 Registers cable speed - and what appears to be Jun 14 1944.     On the face of the gauge- RPM hundreds - Revolutions thousands. 1-10.   Housing diameter is 3 3/8 inches.