This modification was to the Royal Australian Air Force (RAAF) Mark 11 manufactured by Jaeger-Le-Coultre (JLC) but not the Mark 11 manufactured by the International Watch Company (IWC).
The modification, dated February 1957, was undertaken to improve the legibility of the JLC Mark 11, consists of:
1. Fitting a new acrylic crystal with a square step, and
2. Filling a luminized sweep second hand
The civilian contractors, who serviced the Mark 11, undertook the modification at the next reconditioning.
The crystal with a square step can be seen in the following drawing:
The manufacturer of the crystal is not given.
Cheers from the cellar
A link to: Royal
Australian Air Force Watches