Tachometer, Mechanical, British RAF Mk IXG Ref 6A/1191 in Original Box

This is an authentic WWII-era mechanical Tachometer Mk IXG Reference 6A/1191 used in single-engine aircraft of the British Royal Air Force such as the infamous Spitfire and Hurricane fighters. These mechanical tachometers, aka engine revolution or speed counters by the British, were mounted on the instrument panel and connected to the engine by a flexible cable shaft.  This one has a serial number showing a year of manufacture of 1944.

This specimen is in its original box.  Dial measures ~3.5 inches diameter and the unit is ~ 3 inches deep.