Vtg Chronstop Ref 4750

A question for the specialists:

At the beginning of the 1940s, Longines built the reference 4750, a watch with stop seconds - calibre 12.68 Z. The special feature of the watch is both a rotating engraved bezel and an additional rotating ring inside the case around the actual dial.

As far as I know, relatively few examples of this watch have been made and all of them look like the example in the attached technical description from Longines Wittnauer itself.

However, there seems to be one exception: the watch also shown here with two completely different dials. According to a statement from the manufacturer himself, this is possibly a scale for measuring speed.

Can anyone explain in more detail how this should work and what the individual numbers and digits on both the bezel and the ring around the dial mean in detail - how they were used 🤔?

This example also totally threw me for a loop when it popped up. When Peter posted the 1940 technical watches manual a few weeks back I was hoping for an explanation, but alas!

I’m thinking it must have been some kind of very niche application, and maybe a special order - a la the the “nautical miles” stop-second (illustrated in the same catalog) for timing distance form shore in fog using elapsed time between the radio signal and foghorn from US navigational beacons.

If you were the one who contacted Longines re the example, did they comment on the unmarked inner caseback? It seemed quite odd, but given that they issued a new extract, it was presumably original to the watch.

Best of luck figuring it out, it is quite a striking example!

Juergen