RELAY / RICOH SLIDE RULES WITH HYPERBOLIC SCALES
Most of the following information has been taken from David Davis' "Relay / Ricoh Archive" web site. This is found under: www. geocities.com/usra482b/index.html. Relay/Ricoh produced some well made slide rules.
The history of these slide rules started with the Nippon Slide Rule Company that distributed under the name "Nikkei". This Company later became San-ai, and adopted the "Relay" brand name. When the Company
again changed names to San-ai Keiki Co. Ltd., the brand name became "Ricoh". The Relay/Ricoh slide rules were Rebranded, and the same slide rule layouts were sold under different Company names. Many of these
Companies were in the United States. The Relay / Ricoh and the Rebranded slide rules with hyperbolic scales were as follows: Relay 157; Ricoh 157; Alvin 1157; Compass 1325; Lafayette F-686; Lafayette 99-7102;
Lafayette 99-71029; Micronta 157; Scientific Instrument Company (SIC) 1570. More advanced slide rules with hyperbolic and special scales were: Relay 158; Relay DE-1008; Ricoh 158; SIC 1580, and Ricoh 159. The
layout of the scales and other features of the slide rules following the above listed Relay 157, and Relay 158, are identical for practical purposes. The only exception, it seems, is the Ricoch 159. To my knowledge none
of the other brands have a model 159. If someone knows of other 159 models, please let me know.
The following slide rules: Relay 157; Ricoh 157; Alvin 1157; Compass 1325; Lafayette F-686; Lafayette 99-7102; Lafayette 99-71029; Microntra 157; and Scientific Instrument Company (SIC) 1570, all have a LL1' scale on
right end of the C scale. This LL1' is a small scale (about 1/4"). It is used to find natural logarithms when nearly equal to 1, and, for ex when x is near zero.