Airspeed Indicator 450+ Knots Mk 9L Ref 6A/4721 RAF

This is an excellent example of a post WWII-era Air Speed Indicator Mark 9L, Ref 6A/4721, as used in the British RAF fighters Supermarine Spitfire and Seafire.  

Air speed from 0-270 Knots is indicated by a clockwise-rotating pointer, starting at the 6 o'clock position, along the outer perimeter scale.  As the aircraft passes 270 Knots, air speed is indicated along the inner scale up to 450 Knots, with gradations up to 500 Knots.

The indicator measures ~3.5 inches diameter and ~2 inches deep. The glass and case are intact and dial markings are clear and precise. The upward pointing arrow symbol of the Air Ministry can be seen stamped on the rear case.