Harry, for a 6 cylinder engine the indicated RPM should be the test frequency x 20. So if you have a 60Hz test signal the tach should read 1200. Charlie Morgan Beaver State Corvairs At 04:44 AM 8/10/04, Harry Yarnell wrote: >Wasn't there something I read awhile back about using a filament transformer >(remember them?) hooked to the tach, and the 60 cycles would read a certain >rpm. Anybody remember this?