A rare paper instrument for calculating interest.
The web site of the Smithsonian provides background and instructions for the instrument’s use:
“In the early 19th century, Joseph Jelleff of Butternuts, New York, and Gilbert D. Lowe of Hampfield, Pennsylvania, took out patents for mathematical tables that eased calculations of interest. This instrument is a version of their inventions, probably made after their patents had expired.
“The instrument consists of two overlapping concentric discs held together with a metal pivot at the center and attached to a cardboard cover. It is designed for finding the interest on a principal of up to $5,000 at an interest rate of six percent, for times ranging from one to thirty days and then from two months to twelve months. Amounts of principal ranging from $1 to $5,000 are listed on the top disc, going out from the center. Next to this list is a notch in the disc that reveals the disc below. Printed on the lower disc, also going out from the center, are amounts of interest for a given length of time. Lengths of time are marked around the edge of the top disc. Rotating an index on the lower disc so that it points to the appropriate time turns that disc so that the correct amounts of interest are shown in the notch.” (from the web site of the Smithsonian)
An early owner has made some manuscript additions to the tables, and on the movable center wheel has added the word “GOLD” in one of the columns-perhaps a joke in reference to a roulette wheel, which this device somewhat resembles.
McCorison #1747. Parkinson Books, Collection of Gertrude Mallory (Nov. 6, 2004), #222. Examples at the American Antiquarian Society and Smithsonian.
Well used and consequently chipped, rubbed and somewhat worn, but in working order