SEE-SAW
letter scale

This small letter scale is a design by Reginald M. Bowman of Baltimore, Maryland, U.S.A. The scale height is 13 centimeters. A round label is glued to the wooden letter plate. On it is the name "See-Saw letter scale", made in Baltimore, MD, U.S.A .. It also says that patents have been applied for, patents pend.(ing). The US patent 2,508,011 was applied for on April 21, 1947 and was not granted until May 16, 1950. This specimen is quite different from the drawings in that patent, such as the pointer and the aluminum parts. In Equilibrium 2008, issue no.1, pp. 3337-3341 Jan Berning describes three mutually different See-Saw letter scales in the article Bowman's Pendulum Postals. The letter scale shown here is a fourth variant. The scale has two scales on the front and the back. The scale goes up to 8 ounces, and is subdivided per quarter ounce. Below that is the scale with the airmail rate [airmail]. On the back is the rate for 3rd class mail. Below that is the rate for 1st class mail. The 6¢ airmail rate was valid from 1949 to 1955. The first class letter rate of 3¢ was valid from 1932 to 1958. When the 3rd class rate, that is for printed matter and samples, of 2¢ was valid I don't know exactly. This See-Saw letter scale dates from the short period 1947-1950, no patent had yet been obtained, but it had already been applied for. The See-Saw letter scales were made to order. The measuring scales are hand-painted. It is a product of an enterprising hobbyist with a good eye for the details of the bearing. The three See-Saws in the article by Jan Berning weigh up to 9 ounces. The US patent 2,413,166 is mentioned on the letter plate label of two of the variants in the article. This patent, dated December 24, 1946, is in the name of Reginald M. Bowman, but is a design for a letter scale with a hanging letter holder.
Below some more images of this SEE-SAW letter scale from the short period 1947-1950.