H.S. stands for Hydrographic Service. H.S.3 is the Royal Navy code for a deck watch, adjusted for isochronism in a minimum of 2 positions. A deck watch would be checked against the time of the ships master navigation chronometer, which was not to be moved. A deck watch would then be used to check the position of the ship with a sextant or to walk about the ship setting the various timepieces to the correct time.

This particular deck watch is most likely of World War two vintage. Many of these timepieces were sent to the Royal Navy chronometer facility for service in the post war era. It's interesting that the watch does not have a post-war NATO issue code on the back of the case.

I have seen a wide range of prices on these timepieces, as posted on-line. From $650.00 to $1,500.00, with the lower prices tending to sell and the higher prices going unsold for many months. There is one on eBay right now for $650.00 but it does not work and it does not include the wooden box. I think one in good working order with the box would sell for around $1,000.00.