1973 circa Longines Admiral HF Ref. 2301 -1 steel vintage wristwatch on rare fitted NSA braceletThis Watch On the outside this looks like a well designed ,sleek , quality minimalist longines Admirial watch in stainless steel! Hf likely referring to " High Frequency" 28,800 BPH escapment This watch actually hides a cool secret! A feature i was unaware of until now even after 26 years on the bench! pull the crown into the hand setting position and the seconds will Hack (stop) at the 12 oclock position enabling accurate synchronisation of the