This is the only known example of a 3-subdial decimal watch, circa early 1950's.
Fantastic. I am glad David got back to you.Hi Adam,
I emailed DL about it, he says these were special-order only. The dial is most definitely original. It can only fit on an EP40 movement.
As far as what they were used for, I know my grandfather used his decimal for his engineering work. What exactly I'm not sure. Anything that would require timing in units rather than seconds.