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A Disk Calculator

Volume 15, Number 1 (Jan. 1961) Page 23-23

Hodge, Edwin S.

Frederickson (1) and Goldspiel and Conner (2) have described circular calculators for computing intensity ratios and determining composition. One factor discouraging the use of such a calculator is the difficulty in preparing an exact circular two-cycle log scale of sufficient size and accuracy. This problem has been circumvented by the "zerox" (or photostatic) enlargement of the A scale of a 8-in. circular slide rule to a 10-in. diam. The reproduced scale is attached to an aluminum disk, 1/16-in. thick. Relative intensity values for each unit mark of % transmission are tabulated from the customary emulsion Seidel calibration curve. These data are laid out as a circular Seidel % transmission scale on the circumference of a smaller disk 9-in. diam. A special ruler made from rigid transparent plastic is cut so that a radius at the outer end serves as a ruling edge when the two disks and ruler are held concentrically by a bolt, nut, and washer. With the two disks being held together the Seidel % transmission values are marked on the smaller disk at relative intensity positions indicated on the outer log scale.