Here is a large lot of important devices for pilots and mathematicians....including......Deci-lon Slide Rule ($64 used).....DorCliff Super Plotter for pilots--pilots know that a plotter left in the sun or on the dash will warp or become brittle, and useless, but NOT THE SUPERPLOTTER. Specially engineered and designed for long life and durable use, this high performance navigation super plotter with a rotating azimuth makes it easy to plot course lines AND, it is virtually indestructible. It is constructed of bullet-proof Lexan material. It will not crack, warp, break or be affected by extremes in heat or cold, in and out of sunlight. This is a buy-it-once pilot tool. The Dorcliff Super Plotter is a versatile yet simple tool for the pilot (sells at $19 used).....Helix Drawing Set ($13 used) and Helix geometry set ($10 used)....Chemical Engineers Handbook.....The Volume Library of Practical and Cultural Knowledge 1911-1913 (used at $60).