letter scale

This letter scale has two tension springs in the glass tube. First the light spring is stretched in the range up to 20 grams. Then this spring arrives at a stop and the stretching of second heavier spring starts. This spring acts in the range of 20 to 250 grams. The idea of this letter scale is already in the German patent DE365837 of 1919 by Dr. Franz E. Wolf from Malmsheim near Stuttgart in Germany. The actual letter scale differs in a number of minor points from the patent. I don't know who made this letter scale. I suppose the scale was made in Germany. The scale up to 20 grams has a stripe per gram. Above 20 grams every ten grams has a stripe of measure up to 250 grams. The letter scale comes in a nickel plated protection tube with cap. dimensions of protection tube with cap: total length 132.5 millimeters, diameter 13 mm. The letter scale with inwardly shifted letter clamp is 122 mm long, with an idle hanging letter clip the length is 158 mm. The diameter of the glass tube is 10 millimeters. In the past I noticed on eBay that there is also a version of this letter scale measuring in ounces. Up to 1 ounce and stripes per 1/16 ounce the light spring, and above this the heavier spring up to 10 ounces and stripes per ¼ ounce.
Below some more pictures of this special letter scale.