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The Hemmi 257 is a specialized rule designed for chemists and chemical engineers. This rule has a normal complement of scales on the front, but in place of trig scales, the back has a number of special scales useful to chemists, including two scales which give the atomic and molecular weights of substances, scales for temperature conversions, pressure conversions, expansion and compression of gases, and so on.
Scales:
Front: L, A, DF, CF, CIF, CI, C, D, LL3, LL2, LL1
Back: Ch(A~M), Ch(N~Z), M1, M2, °F, °C, °K, F(t), Kg/cm2, mm Hg, in. Hg Vac, tw