Mark VA And VB Stop Watches

SPLIT-SECONDS STOP WATCH
MARK VA AND VB
24. These have a split-seconds chronograph action, may be carried in an aeroplane, and are
of use in connexion with performance tests and navigational purposes. A Mark VA (Stores
Ref. 6A/129), and a Mark VB (Stores Ref. 6A/140), are illustrated in figs. 4 and 5 respectively.
They are alike except for scale markings, are of the eight-hour keyless type, with beats to one fifth
part of a second, and the two centre seconds-hands are rated to one revolution per minute. It will
be noted that the Mark VB has a scale which is divided to a base of 360º, and may be used in
connexion with direction finding.

The above abstract is from Ministry of Aviation AIR PUBLICATION 1275, VOL 1 SECTION 1-
CHAPTER 13

I have one of the Mark VB type although stores reference engraved on the back differs slightly as
it is 6B/140. The information above was provided by the RAF Hendon Museum, but they could not
amplify further on how the watch was actually used for navigation. They said it was from the 1920s
period and do not have an example. It is the intention to give the watch to them to go into the
collection, and I would like to know if anyone in this forum can supply any information regarding
how exactly it would have been used as a navigational tool.
I have in the past shown the watch to WW2 ex-navigators and ex-bomb aimers, but none could
tell me how it was used.