Airspeed Indicator, Maximum Allowable, Type L-7A w/Mach Limiter, Kollsman 1214DX
This is a Cold War-era Airspeed Indicator, 0-650 Knots, Maximum Allowable, Type L-7A, made by Kollsman and used in aircraft of the US Air Force such as versions of the fighters F-86 Sabrejet, F-80 Shooting Star, F-84 Thunderjet, F-89 Scorpion, F-94 Starfire, trainer T-33, and versions of bombers B-47 and early B-52's (see illustration of B-52 panel).
The main pointer rotates clockwise as the airspeed increases. The horizontally-rotating drum above center is graduated in 2 knot increments to indicate airspeed more precisely, and rotates right to left as airspeed increases within each 100 knot range. The mach number limit is adjusted for the specific aircraft model by turning the inset screw on the rear case prior to installation. As the screw is turned, a very small black index pointer travels along the perimeter of the dial between 350-530 knots setting the mach limit between 0.6 to ~1.3 mach. As that screw is turned the striped maximum airspeed pointer moves along its prescribed range. When in flight and the airspeed of the aircraft reaches the striped pointer, the aircraft is at its maximum allowable airspeed or maximum allowable mach speed, whichever is less.
This instrument is stamped with a service date of December 1959. The case, glass and dial are in exceptional condition for the age of this indicator. Measures 3.25 inches diameter and 5 inches deep.