Before the development of digital calculators, multiplication, division and other mathematical operations were commonly accomplished with slide rules such as seen in the North case on the opposite wall. Unfortunately, common slide rules were only accurate to a couple of decimal places. Edwin Thacher invented a slide rule with scales equivalent to 66 feet in length instead of the 10 inches of common slide rules. Marketed by Keuffel & Esser, Thacher’s Calculator enabled calculations to four or five decimal places. This made it a valuable tool in science, engineering, business and commerce. The cylindrical slide rule on display was used in the local timber industry for calculating loads for schooners, lumber production, etc.
The calculator's brass framework and 4" diameter cylindrical rule sits on a mahogany base 21 5/8" long x 5 5/8" wide and comes with a custom fitted mahagony case. A photo of the closed case shows the box joints at the corners and a paper label placed on the lid by the donor(?). The slide rule has paper scales printed from engraving plates calculated to seven decimals and accurate to ±0.0001”. The scales are discolored from reaction of the paper and brass framework. The right end of the cylinder is marked with the manufacturers logo, the patent date, and engraving information. The catalog image is from Clark McCoy's K&E Catalog site, where scans of the complete catalog and many others are available.
For your further interest a link is provided to a copy of the Operator's manual for the Thacher Calculator at McKoy's K&E catalog site.
© R. Paselk