In the nineteenth century, several American inventors devised moving tables that allowed one to calculate interest. This is the U.S. Patent Office model for a device designed to calculate the amount of interest upon any amount less than one thousand dollars for any number of days less than eighty-five at two rates, six and seven percent. It was invented by Albert C. Pierson of Rahway, New Jersey.
The instrument has three ten-sided rotating prisms, with the sides of each prism marked at the top with the digits from 0 through 9. The rightmost prism represents units, the middle one tens, and the leftmost hundreds in the amount of money borrowed or lent. Each side of each prism has two columns of 84 numbers, corresponding to interest charges for 1 to 84 days. The left column has interest charged at 6%, the right at 7%. Setting the prisms to the correct amount and then summing the numbers on the three prisms for the appropriate number of days gives the interest. A rotating strip on the left allows one to determine the number of days between two dates of the year.
This is the model for the first of two patents taken out by Albert C. Pierson (probably 1836–1870). Both relate to calculation.
Reference:
A. C. Pierson, “Improvement in Calculating Machines,” U.S. Patent 62,882, March 12, 1867 (the machine illustrated by this model).
A. C. Pierson, “Improvement in Calculating Machines,” U.S. Patent 73,995, February 4, 1868.
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