The 6B is the RAF Stores Section reference and refers to Navigation equipment. The other numbers relate to the specific item, in this case this watch and known as the Ref. It is likely that other manufacturers also provided watches to meet the specification and shared the same section and ref.
Another example was a Douglas Protractor which had a very low number 6B/47.
Around 1967 all Service stores were recategorized with a NATO Section and Ref. Typically nnnn-nnnnnnn. In the case of the watch the section would have been 4 numbers followed by the same reference numbers.
The H 67 may be the company reference and the 3800 the individual serial number.
In theory you could go to any NATO Store and demand a piece of equipment using the unique Section and Ref. It could then be provided through the interservice system.
Last edited by Pontius Navigator; 1st Feb 2019 at 17:59.