Marked: nameplate reads: "Radio Wavemeter and Kolster Decremeter / Made for Navy Dept. (BU. S.E.) by / National Electric Supply Co. / Washington, D.C. / Req. 1702 N.S.A. Cont. 36904 5-23-18 / Type CN1215 Serial No. 111 / [lambda] 100-3500 meters". Navy wavemeter and Kolster decremeter with cover. Main tuning control is calibrated in four sections from 100-3500 meters. (100-260, 250-600, 550-1400, 1300-3500 meters) Vernier scale has a .30-0-.30 calibration (S1 and S2), current squared meter has 0-100 scale, other panel controls include a buzzer, buzzer battery, crystal detector (xtal missing), three way switch for detector, meter, and buzzer. Four plug-in coils are used, three are mounted in top of the unit. Ref: Clark Collection: class 2, book 1. Navy Type Nos., 1918.