Notes: "The K&E “polyphase” refers to a slide rule that has an inverted C scale, the almost ubiquitous CI scale. The 4088 Polyphase Duplex adds CF, DF, and CIF scales, to facilitate chain calculations. As its name implies, it is also a duplex slide rule, and calculations can carry from one side to the other if necessary. K&E made the model 4088 from 1913 to 1939. Based on its serial number, 452201, this one would have been made in the mid-1930s. "