That's a Speedmaster reduced, I suppose it's a relatively modern watch compared to the Speedmaster lineage.
As far as I'm aware, it only came with the 1 movement, the calibre 3220, which is fitted with a piggyback chronograph module.
Edit- just checked the reference, it's 3510.50, some checking does give more information on a range of movements , with a 1143 being fitted post 1996, either way it still had an chronograph add on movement.
Bit more info here-
https://www.sellwatcheslondon.co.uk/the-omega-speedmaster-automatic-reduced/
Where and how did you come by this watch?
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