Stew,
I just read a little in Wikipedia...
No sure explanation regarding the name's precise background, as they moved to N.Y.C. In the late 19th century, where they actually founded Wittnauer...etc. etc.
And by the time these Chronos were designed they were already with Longines.
Doesn't matter.... I found the same model watch with a bezel saying Tachymeter.....with a Y.
So no more wondering really necessary, dear Stewart. I guess... never mind....
Our dear Mister/Monsieur/Herr Heuer too, for example, as so many others in that beautiful prosperous region, was brought up in German as well as in French ....
So, I guess, back then at Wittnauer / Longines they must have thought and written it either way.

O

Well spotted Olaf.. interesting.. I wonder what the reasons for
: this may be!

: Stewart
: - Heuerville