Tachometer Type E-4 Weston 545 A-20 Havoc
Here 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 diameter by 3 inches deep.