Aerial Dead Reckoning Computer, U.S. Army Air Corps. Type E-6B . Dials all seem to work with no problem. By Harry H. Knepper Inc. 
Aerial Dead Reckoning Computer, Type E-6B Spec. No. 94-27892 This slide rule was developed by Phillip Dalton with the help of PVH Weems in 1933 and introduced into the Air Corps in 1940 under the designation E6-B. 
In 1943 the name changed because of the standardization of equipment and Army and Navy took the designation NA-C-74. - HARRY H. Knepper Inc.. - G. Felsenthal & SONS 1942 - Keuffel & Esser Co. - CRUV Mfg. Co. - STANLEY Mfg. Co. 1942