Scientific Instruments 1510 and 5510 Astrolog

The Models 1510 and 5510 Astrolog were produced by the Japanese Company Relay/Ricoh Ltd. for the American company Scientific Instruments Co. seated on Berkley, CA. during the 1960's. As most of the rules made in Japan, this was fabricated with bamboo, coated on all sides (except the ends) with white celluloid where scales were engraved, and everything held together with metal posts. The all glass indicator was screwed to plastic ends, and was customized engraving the scale symbols on these glasses, a unique characteristic of the Scientific Instruments slide rules.

The 7 inches long - 5 inches long scales 5510 model was the pocket version of the 14 inches long - 11 inches long scales 1510 model, which was a clone of the Ricoh 151 Multilog, the Sans & Streiffe 312, and of the Relay DT-1600, . The Astrolog family is very well designed for Advanced Science and Engineering work. The A-B and C-D scales on the 1510 model are extended at both ends, making these scales 11-inches-long. The 5510 model lacks these extensions on scales A-B and C-D.

The 25 scales on these models are: LL-0, L, K, A [ B, S Cos, ST, T Cot, C ] D, DI, P, LL0 on the front face, and LL-1, LL-2, LL-3, DF [ CF, CIF, CI, C ] D, LL3, LL2, LL1 on the back face.

Even though these rules have a serial number, I have not found yet a reference to figure out the possible manufacturing date. Both have the copyright year engraved on the edge: 1961, so the only affirmation that can be made by sure is that both rules were manufactured between 1961 and 1964, assuming this last year because the company's logo was changed in 1965.