Faber-Castell Darmstadt Addiator 111/54 & 67/54Rb

Faber-Castell was the only slide rule manufacturer that integrated an adding- subtracting device, the Addiator, to some of their models. The Models Darmstad 111/54 and 67/54Rb are two of several that had integrated an addiator on the back face.

The Darmastad 111/54 was produced in Germany from the early 1950's to late 1960's. I did not found the exact year the production of the 111/54 with integrated addiator began. I only found two patents for this kind of slide rule dated 1959 and 1961. So is possible to conclude that the production of these rules began in 1960-1961. The specimen in my collection was fabricated in June 1961. The Darmastadt 111/54 rule was fabricated all plastic, the cursor is also all plastic with two gauge lines.

The Darmstadt 67/54Rb was also produced in Germany in the early 1960's. N exact year the production of the 67/54Rb with addiator integrated began, but I found some pictures of these rules fabricated in 1961. The specimen in my collection was fabricated in November 1968. The Darmastadt 67/54Rb rule was all fabricated all plastic, with cursor also all plastic but with four gauge lines.

The System Darmstadt refers to a Mannheim or Reitz type rule with log-log scales added. The Darmstadt rules have the scales S T A [ B K CI C ]D P on the front face and the scales: [ L LL1 LL2 LL3 ] on the back of the slider. Darmstadt slide rules usually have, on the back, two small windows with hairlines corresponding to the two index positions on the stator. This allowed the use of the scales on the back of the slider without turning the slider over.

References:

• Holland, Peter: Rechenscheiber/Slide Rule. A.W. Faber - A.W. Faber-Castell. Modelle, Typen, Skalen/ Models, Types, Scales. 2020 Digital Edition V 8.0. (This an extensive reference of Faber Castell rules models) Rechenschieber von Faber-Castell (sliderulemuseum.com)