Thacher's Calculating Device


Thacher's Calculating Device


Calculating Devices


This early relative of the slide rule has a cylinder 4 in. in diameter and 18 in. long that rotates and slides in and out between the array of twenty equally-spaced parallel bars. The bars have a scale with numbers spaced logarithmically, as on a slide rule’s multiplication scales. The cylinder also has a logarithmic scale engraved lengthwise on it. The net effect is that of a very long slide rule, allowing calculations accurate to four to five digits to be made. In 1934 this instrument was sold by Keuffel and Esser for $80.00.


Property of the W&L Physics & Engineering Department



“Thacher's Calculating Device,” Digital Exhibits at Washington and Lee University Library, accessed May 26, 2018,