pen-sized letter scale

This is an old pen-sized letter scale. The specimen isn't complete anymore. A part of the spring clip to hold the letter, is gone. The expected writing part even has disappeared completely. Most likely, this letter scale is described in a German patent from 1934. The patent number 602407, mentions Adolf Zoeller from Nürnberg as the inventor. The application of the patent dates December 1932. The square shaped scale has the imprint D.R.P.a. This is the abbreviaton of Deutsches Reich Patent angemeldet, meaning: German patent applied for. Therefore, This pen scale dates from the period December 1932 - August 1934. The initials of Adolf Zoeller are put into a logo: A Zet. At the end side of the cap is another logo imprinted with the characters W, F, D, and G. The proper sequence could also be W, D, F, G. I don't know the meaning. The scales unit is constructed solidly. The fine tuning nut is fixed at the proper position with a little pinch. The range is 50 grams. At one side of the square chart part a stripe for each gram is given. At the adjacent side the value per five grams is given in figures and a stripe. Below some more pictures of this pocket scale are presented.