Tachometer Type E-4 Weston 545 A-20 Havoc H-21 made by US Gauge

made by US Gauge

but utilizes an electro-magnetic compensation system

made by Maxwell Smith Co

although they could be retrofitted to other models

I is a straightforward gyro-magnetic compass using magnets for deviation correction of the detector unit (usually located in the tail or wingtip)

Tachometer Type E-4 Weston 545 A-20 Havoc H-21 made by US GaugeHere is a WW2 vintage electrical Tachometer measuring up to 3500 RPM. This is the type used on the Douglas A 20 Havoc attack bomber (see photo of instrument location on the A 20 cockpit panel as illustrated in its flight manual) as well as the C 45 Expeditor transport (both aircraft used 2 each). The anchor symbol of the US Navy appears on the rear of the instrument, so it may have been used in an aircraft of the US Navy. Measures 3. 25 inches