GB688639A - Improvements in logarithmic calculators - Google Patents

Abstract

688,639. Calculating-apparatus. ABEILLE, M., and AQUILECCHIA, V. April 11, 1950 [April 12, 1949], No. 8934/50. Class 106 (i). A pocket logarithmic calculator comprises a rotatable drum 6 mounted within a casing 1 and marked on its periphery with logarithmic and cologarithmic (colog. x=log. 10-log. x) scales read by a magnifying eyepiece 7 against a fixed index mark on a window 8. A movable index is frictionally engaged with the drum; as shown, this index is marked on a coaxial disc 10 provided with a frictional coupling 14 adjustable by a set-screw 15, and with a spring detent 18 normally positioning the disc with its index accurately in register with an index mark at a window 5. A finger pinion 9 is engageable with and drives the drum 6 alone, and a pinion 11 drives the disc 10 and with it the drum 6. Multiplication is carried out by adjusting the drum 6 by means of its pinion 9 to bring the multiplicand on the log. scale to the index mark in window 8. The disc 10 and drum 6 are then rotated together until the multiplier on the colog. scale registers with the index mark. At this stage, the index mark on the disc 10 will have been shifted away from the index at window 5 by an amount representing log. 10 - the logarithm of the product. To find the product, the drum 6 is restored to zero by means of its pinion 9, and the disc 10 then restored, continuing its previous direction of rotation. This rotation of the disc 10 is transmitted to the drum 6 which now shows the product on its log. scale at the index line on window 8. The main graduations of the scales are repeated by scales on the circular face of the drum, windows (not shown) being provided in the casing for reading these scales. The drum 6 also includes log. scales of the trigonometrical functions and uniformally graduated number scales.