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Mark I, II, III, and IV constituted a strange category system for Swift Instruments. Basically, Mark II products were the best of the Porro-prism models, and Mark I was somewhat lower quality and cost — for example, using Bk-7 prisms. Still, the Mark 1 models were perfectly good instruments...

Hi Jerry, Welcome to Birdforum (the talking part ;)). Your binoculars were indeed made in 1975 as indicated by the first two digits of the serial number. I've attached a picture of your Model 801 from Swift's 1975 catalog, where you can see that it's one of four Mark I "Wide Angle"...