09-005. French, 1st quarter 20th century, signed on the faces "CALCUMETRE G. CHARPENTIER, BREVETE S.G.D.G., " and described in the 1909 Keuffel & Esser Co. catalog as follows: "The Charpentier Calculator is a circular slide rule 2 3/8 in. diameter, with a circular slide which is revolved and set by the handle. This instrument being made of metal is but slightly affected by atmospheric variations. On the face of the calculator there is a logarithmic scale on the slide corresponding to another such, external to it on the body of the rule. On the surface within the slide are the square roots in two circles, one from 0 to 3.162, the other from 3.162 to 10. They are made to coincide with the outermost scale by means of an index. On the other side of the rule there are three scales, and outer one of equal parts and two inner ones of angles from 2 to 90 and from 0 to 45 respectively; the latter two give the sines of the first and the tangents of the second on the scale of equal parts, by means of an index. The indexes on the two faces correspond, so that the logarithms of the numbers on the logarithmic scale can be read on the scale of equal parts." This Charpentier Calculator is in very good overall condition.
