Notes: "Gebruder Wichmann only sold other company’s products. This slide rule is almost a Rietz slide rule, except no CI scale. It has interesting trig scales on the back of the slide, with the S scale is on the top and the T scale is on the bottom. Each of the trig scales is referenced to the scale it is next to: the S scale to the A scale and the T scale to the D scale. This allows the S scale to cover a range of angles that normally requires both an S and ST scale: 35 minutes of arc to 80 degrees. The tangent scale runs from 5.7 degrees to 45 degrees, but for small angles you would just use the left half of the sine scale. "