Signedplate on top: LEEDS & NORTHRUP CO. / PHILADELPHIA, PENNSYLVANIA / MADE IN U.S.A. / CAT. NO. CLN-631211 (L&N logo) SERIAL NO. 413178
FunctionSlide wire resistances or potentiometers are a very precise form of variable electrical resistance. A long wire of metal is wound around a spool or drum, and the point of electrical contact with the wire varies as it is turned. This varies the electrical resistance. The scales on the drum and the vertical circular scale are to determine very precisely the length of wire that is currently active.
Such precise resistances were used to regulate and measure electrical currents.