Postamatic postal scale
The Postamatic Postal Scale is a pen-shaped cylinder with an interior spring. The letter was attached to the clip at the bottom, and the scale was held upright so the spring would contract and indicate the rate. Rates for airmail and first-class postage valid between July 6, 1932, and July 31, 1958, appear on the scale’s transparent yellow body. A silver clip is attached to the body of the scale so the user may carry the instrument around in a pocket, hence the name 'The Pocket Postal Scale'.