My mentor Erich is a good teacher and he takes teaching me seriously. That implies giving me some theory lessons as well. Here I learned to calculate the relationship between wedge position, drum setting and set value.
Details can be found in the German version of this post: The 2-unit difference can be read from the drum, lowermost row: (38) – (112) = (111) With this value we can calculate the 2-unit width at 8½ Set to 1×0.0075″+11×0.0005″ = 0.0130″ and thus 1 unit to 0.0065 inch or 0.16 mm.
A bit simpler at 11¼ Set: (38)-(13)=(25), thus 2×0.0075″+5×0.0005″ = 0.0175″. 1 unit is 0.00875 inch or ca. ¼mm.