Omega speedmaster moonwatch tachymeter - why the difference?

[JPSP]

Hi all,

Just curious. Probably a silly question. I've posted this question in another forum and thought maybe someone here has an answer

I noticed that the speedmaster moonwatch chrono co-axial 44mm (with 3 subdials) has the tachymeter that starts from 1000 whereas the one with 2 subdials, fitted with calibre 9300, starts from 500. Any reason why since both are also moonwatches?

cheers

james

[Everdying]

actually it doesnt start at 1000.
'Base 1000' is the tachymeter scale used.

both are still the same scales,  but i guess the former doesnt want any misunderstandings as to what Base is used