Just a few days after someone suddenly realized they had to know what rpms the engine was turning? I'm feel pretty sure there were already tachs and / or other calibrated gear drives in use for marine engines, industrial gizmos, measuring wind speed, etc. long before the auto came along. Perhaps the question might better be, "When was the first hot rod made?" and then add a couple of days after that! Gary
Tachometers have been 'around' almost since the beginning, but until the advent of electronic units in the early 60s were a bit uncommon as some sort of cable drive was needed with the then-mechanical units. Most early units were driven either off a specialized distributor or off the rear of the generator.
The Jalopy Journal
