This cylindrical slide rule was designed to perform exact mathematical calculations for engineers, architects, actuaries, scientists, and financial institutions. With radii of 60 and 30 feet, the scales on this device could provide accurate calculations down to five decimal places at a time when regular slide rules could only provide results to the third place. Made out of ivory instead of boxwood, the plates would not warp or shrink over time or with changes in temperature. According to the accompanying instruction manual, Thacher’s Calculating Instrument could perform the “greatest variety of useful calculations with unexampled rapidity and accuracy,” and “professors and students of schools and colleges will find it the most valuable aid to mathematical study that can possibly be desired.”