How do I check the accuracy of a mechanical speedometer?

Most mechanical speedometers are calibrated to register 60MPH (100KPH) when the input speed to the instrument is 1000 RPM.

NOTE: No ratio adapters are used in this test.

The known speed rotating device (e.g. an electric drill that turns in the proper direction to cause the speedometer to indicate) should cause the speedometer to indicate in relation to this ratio. EXAMPLE: if the drive (rotating device) is 1000 RPM, the speedometer should indicate 60MPH; if the drive RPM is 500, the speedometer should indicate 30MPH; if the drive RPM is 1200, the speedometer should indicate 72MPH.

The odometer should register one (1) mile at 60MPH indication in one (1) minute.

If the instrument does not function correctly, look for possible flexible shaft core breakage. Also, if a ratio adapter is used in the system, it must be checked for function independently.