Tachometer Type E-4 Weston 545 A-20 Havoc H-21 with an antenna wire connect

with an antenna wire connect from the top of mast to the top of the tail

The instrument would indicate the hydraulic pressure within the undercarriage system of the aircraft

made by Maxwell Smith Co

A gallon of avgas is ~ 6lbs

but utilizes an electro-magnetic compensation system

Tachometer Type E-4 Weston 545 A-20 Havoc H-21 with an antenna wire connectHere 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