Well, it's obviously an Omega movement. Case was made by the Dennison Watch Case Company in England and the serial number dates the movement to approx 1930.
The case isn't hallmarked so it would most likely be brass with gold plating.
The caliber (or movement) number under the balance can't bee seen, but a measurement across the movement will help to identify the caliber, maybe a Caliber 37.6L.
While they didn't have "Seamaster" or "Speedmaster" names for the watches in the 30s, this may have been referred to as an "Omega Art Deco Lépine" based on the period and the style.
Due to the limited number of pocket watch collectors, value is not that high and the gold chain adds little value as it's only worth the scrap gold content.
The best thing to do is find a reputable watchmaker and have it serviced but not "restored".
And the you can enjoy it as your grandfather obviously did.
Cheers
Jim
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