It's what we call a transition Constellation. It's from the early 70's when Omega was switching over from the 55x/56x/75x calibers to the 10xx series. If it has a 56x (561 or 564) it's worth a couple hundred more than if it has a 10xx (1011) inside. I'd say it's already close to the maximum for a 1011 powered watch.
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