Sterling letter scale
The Sterling letter scale is protected by an American design patent with the number 219,712. It dates from January 12 1971. The application was made September 11 1969. At the upper side a copyright and the year 1968 is moulded into the plastic. The four figures of the design patent strongly resemble the actual scale. Only the knob for fine tuning the indicator is given a slightly different form. Except the spring, the whole scale inclusive the mechanism, is plastic made. The chart goes up to 17 ounces. Odd enough, the first class rate stops at 14 ounces. The airmail rate even stops already at 8 ounces. Molded at the upper side is a text stating Sterling Plastics Co. will deliver new rate labels for 25c. Also a Sterling Plastics logo, the characters S P, is moulded on this
back of the scale
