Could not resist this one A ref. 2175/3 from 1944 with a caliber 23.4 SC. This one is one of the later ones with a plain back, water-resistant case with a lead gasket. The Non Magnetic refers to the later ones from after 1941 where they used monometallic balance and self-compensating balance springs in anti magnetic alloys. Not much found on this ref. so if any one can help with info's, old add's it will be appreciated A 1940's add. with credit to @Tire-comedon