Nestler Rietz No. 20/1

The System Reitz No. 20/1 slide rule was manufactured in Germany in the period 1931-1947, according with the information I found in the Website of the German-speaking slide rule collectors www.Rechenschieber.org. The lack of printed or engraved serial numbers on many Nestler models, as well as product catalogs are very difficult to find, make difficult to determine fabrication years with precision. The Rietz 20/1 model can be seen in the 1938 catalog.

The Rietz No.20/1 was fabricated with Mahogany covered with white celluloid screwed to the wood body in some models (Early models?) and glued in others, glass indicator metallic frame. This rule could be considered a variation of the No. 23 family, where the reverse scale CI is not present. The scales on the Rietz No. 20/1 are Centimetres K, A [ B, C ] D, L Inches on the front face, and [ S, ST, T ] on the slider's back. These trigonometric scales are divided in degrees-minutes. On the rule's back face there is a very dense table with unit conversions, equivalences, and materials properties, which makes that think this rule was created for the engineering field.

There were some variations in the Rietz No. 20/1 during the 16 production years. The model in this collection has the top cubic triple logarithmic scale divided from 1 to 1,000 (i.e., 1 to 10 to 100 to 1000), and the quadratic double scales divided from 1 to 100 (1 to 10 to 100). Also the single and double logarithmic scales have extended scales at their ends. Some No. 20 models do not have these characteristics (Early models?). As many other Nestler rules, this model does not have labeled the front scales, only the scales on the slider's back are labeled.