pocket letter scale & ballpoint

This combination of a ballpoint and letter scale was invented by Werner Wagener from Solingen, Germany. A lot of effort was put in the intellectual protection. In 1952 a Gebrauchsmuster DE1643667U was applied for and granted to a predecessor of this pocket letter scale. Next a patent was applied for in 1953, this was only finally granted in 1955. This is patent DE926882. Later in 1956 an official addition to the patent was recorded in patent number DE939899. I guess this letter scale has not been long on the market. Postal scales in the form of, or combined with, a pencil or a ball pen were invented by others earlier. The uniqueness of the Werner Wagener letter scale is that the weight of the letter balance itself is used to check the mark on the scale at 20 grams and that the weight of the closure cap of the ballpoint is used to set the mark of the letter scale at the position of 5 grams. The letter scale has a brass slider with a small window shaped opening for placing it precisely onto the red stripe of rhe moving interior part. This slider is shifted over the pen to the desired position for the weight limit of 20 or 5 grams. This pocket letter scale indicates only whether the letter weighs lighter, is equal to, or is heavier than 20 grams. Or in the position of the air mail weight limit of 5 grams, whether the letter weighs lighter, is equal to, or is heavier than 5 grams. The need to always check and adjust the weight limit is rather cumbersome. I don't know the weight of the decreasing ink filling in the container of the short ballpoint, but it is less than 0.2 grams. The Werner Wagener pocket letter scale was delivered in a cardboard box with removable lid and a separate manual with text on one side and drawings on the other side.
Below are some more pictures of this Taschenbriefwaage or this pocket letter scale.