Looks like an Omega ladies pocket watch, converted for use as a man’s wrist watch by soldering on the lugs.
You might find that the movement dates to the early 1900’s, with the conversion being done in the 1910’s or 1920’s, depending on which part of the world your grandfather came from. Very common thing.
We cannot tell you much more without pictures of the inside of the watch. Best to take it to a watchmaker who specializes in pre WWII watches.
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