.Old Metal & Brass Adjustable Level*A.T.Koopman*Chicago

Description/Condition: You're bidding on an interesting old iron & brass adjustable level for some kind of special use . The level is stamped on adjustable brass plate "A.T. Koopman, Chicago" & "Pat Appl For". The glass bubble on top of arc is in good condition, brass and has two small adjustment screws. I couldn't find any information on a patent by A.T. Koopman or any examples of simular levels. The level is 13 inches long