The tach determines the maintenance items such as the ADs and 100-hour inspections. The Hobbs meter, like anything mechanical, can fail.

That’s what happened when [Glen Akins] came across a tachometer for a jet airplane, which he promptly turned into a unique CPU utilization gauge for his computer.

During the mid-'90s, you'd be hard pressed to find a modified Honda without an Auto Meter Sport-Comp Monster tach perched menacingly upon its dashboard. Check out this old school flash back ...

Gauges -inc: Speedometer, Odometer, Oil Pressure, Engine Coolant Temp, Tachometer, Oil Temperature, Transmission Fluid Temp, Engine Hour Meter, Trip Odometer and Trip Computer ...