Charvoz - Roos SR-108 & 109 Duplex

The SR-109 Duplex slide rule was manufactured in the United States initially by the Roos Company in 1940, and since 1945, after a fusion with Charvoz Inc., by the Charvoz-Roos Corporation until 1953, year this corporation was sold. Fabricated with mahogany coated with white plastic, all plastic cursor and held also with plastic braces. This model was also commercialized under other brands: Post 1457 Mannheim Trig, Arthur Brown & Bro. 7996A, Engineering Sales Co., No. 6004,

It's 13 scales, formulas, tables, made the SR-109 appropriate for school and professional work. The scales on this rule are: T Cot, DF [ CF, CIF, CI, C ] D, S Cos, ST on the front face, Units transformation tables + rule settings, Inches Fractions-Decimal table, [ B, K, L, C ], and Trigonometric Identities on the back face. The entries in the trigonometric identities and the fraction-decimal conversion tables are identical to those in the Acu-Math 511 - 600, or Acu-Math 400B rules, but the conversion units table in the SR-109 does not have 32 entries as the Acu-Math models, but only 24.

During the SR-109 production years Charvoz-Roos fabricated unbranded rules with not known purposes, the specimen in this collection is one of those without brand, model or serial number, only the Made in USA label, so it is not possible to state with precision when it was fabricated, but observing the model in the ISRM Charvoz-Roos page, this model may be fabricated between 1941 and 1946, presumably to replace foreign imports of slide rules during WWII.

The SR-108 Dual 10"/5" slide rule was also manufactured in the United States by the same years of the SR-109. As the SR-108 user manual says: combines the convenience of the 5-inc pocket size with the accuracy of the standard 10-inch rule. With the same structure as the SR-109 a wood body white plastic laminated, was hold with all plastic braces, and also equipped with an all plastic cursor identical to the one in the SR-109.

The 14 scales on the SR-108 made it a good tool for students and professionals. The scale set in the SR-108 is not identical to the SR-109, it misses the folded scales DF-CF- CIF, ST and CI, but this is replaced by identical scale DI. Also, because it size, it does not have the trigonometric identities table and neither the equivalences table, it only has the fraction conversion table.But it has other additional, interesting, and not very common scales: C1-D1 running from 1 to square root of 10, and scales C2-D2 running from square root of 10 to 10, and together make complete 1 - 10 scales!

The scales set on the SR-108 is: K, A [ B, S, T, C ] D, DI on the front face, and Fraction-Decimal [ L, C2, C1 ] D1, D2, D on the back face. The rule in this collection was fabricated for the Frederick Post Co. with the model number 1442, but also was distributed with the brand Engineering Sales Co. No. 6002. It does not have a serial number to determine the exact fabrication date, but according with the user manual coming with this rule has a copyright year 1944.