Hi Joe

Sounds like a Cal 15 Monaco - note that the small details you mention are important.

The Cal 15 ref 1533 (check for this number between the lugs) has a small constant seconds register the same colour as the dial on the left hand side near 10 0'clock ("Monaco" was written under this register), and a 30 min register in a contrasting colour at 3 o'clock.

Two dial colours were available- a blue (1 x white 30min register) and a silver mirrored dial (1 x grey 30min register).

The base back should read "tool no 033" (not 333).

I've never seen one with the spelling "chronographe".

See the OTD pages....is should like the two examples there.

Having said this, there are some quirky & genuine variations on the Monaco standard dials......without seeing a picture I couldn't be sure to advise you, though.

Good luck

Stewart.