Aristo Rietz 99 and 89

The Aristo Rietz 99 and 89 models was produced in Germany from 1950 to 1970. Fabricated from high grade PVC (Astralon/Aristopal), was equipped with a four lines plastic cursor, This models were commercialized as slide rules of traditional pattern with an arrange of scales adequate for civil engineers, architects, designers, foremen, technicians, and craftsmen.

In 1902, the German engineer Max Rietz modified and enhanced in the locations of the scales the System Mannheim with a cubic scale and a mantissa scale on front: K A [B C]D L, trigonometric scales S and T, and gaps with index lines on the back side, so the slider could be read on the back side without turning the slider in the slide rule. Years later, in 1925 he added a reciprocal CI-scale and a scale ST for small angles. This arrangement of scales is known as the System Rietz.

The Aristo Rietz 99 and 89 have the scales: K, A [ B, CI, C ] D, L on the front face, and [ S, ST, T] on the back of the slider. according with the engraved serial numbers at the back face, the 5 inches rule was fabricated in 1959, and the 12 inches rule in 1961:

References:

• Mosand John: A Brief History of the Aristo Studio Slide Rule. http://www.oughtred.org/jos/Mosand_BriefHistoryOfTheAristoStudioSlideRule.pdf

• Aristo: Product Catalog 1969: https://drive.google.com/file/d/1il3ty5j3n2rC4mHHBqag1jX788X1EmNd/view?usp=sharing

• Aristo-Werke, Denert & Pappe KG: 100 Years of Aristo Slide Rules 1872-1972, Hamburg. 1972. https://drive.google.com/file/d/1AYMhF20TCHU_nUQLkx0RaJ9pNK1vTyic/view?usp=sharing