In 1970 there was a revision to defense standards 66-4, 'DEF-STAN 66-4' by the Ministry of Defense, 'MoD'. Although a simple change, it allowed for pilot's chronographs to feature two "push pieces." Prior to this the MoD designs called for single button chronographs that required specialized movements, these were mostly by Lemania. Four brands came to the party; Hamilton, CWC, Newmark, and Precista. These brands utilized the Valjoux 7733 movement for their MoD chronographs and are known as the 'Fab Four' by collectors. The T in the circle refers to tritium lume used on the dial and the arrow or "Broad Arrow" signifies the watch was for the British Ministry of Defense. Brand: Hamilton Reference: 0552/924-3306 Material: Stainless steel Dimensions: 38mm diameter; 12.5mm thickness Crystal: Plexiglass Lume: Yes, tritium Caliber: Hamilton signed Valjoux, manually-wound, caliber 7733 Lug Width: 20mm Box/Papers: No Location: Los Angeles Website: keepiece.com Price: $3999 CA residents may be subject to sales tax CONDITION & SERVICING \-The dial is matte black color and is in excellent condition. \-Hands are in very good condition, both being even in color. \- Case is unpolished, edges are sharp. Minor hairlines but overall a really nice example. \-Service history is unknown but is running to spec. TIMESTAMP: https://imgur.com/a/1DEcx4g