Frederick Post 1461 Electrical

The 1461 Electrical rule was produced in Japan by the SUN-HEMMI Bamboo Slide Rule Company Ltd., and commercialized in the United States by Frederick Post Company from 1932 to 1942(?). This rule was fabricated from a large-diameter variety of bamboo grown in Kagoshima Prefecture on the island of Kyushu, coated on all sides (except the ends) with white celluloid, and held together with metal posts. The glass indicator has a metal frame screwed to plastic ends. 

The Post 1461 Electrical is a very rare rule that was discontinued before the beginning of WWII, and the model number used for the pocket companion of the Post Versalog 1460. It was a version of the HEMMI 153 (1933-1967) designed in 1929 by Sadatoshi Betsumiya and Jisuke Miyazaki. 

Originally designed for the use of electrical engineers, it has the unique characteristic of including the Gudermannian scale G(theta), useful to compute hyperbolic functions using the regular trigonometric scales. It has also scales P and Q to find the magnitude  z  of a vector given the components (x, y), or the value of one of the components given the vector's magnitude and one component (Pythagorean Theorem). It has also scales for angles in degrees and radians (0 - 90o)

The scales set on the Post 1461 Electronic is:  L, K, A [ B, CI, C ] D, T (tau), G(theta) on the front face, and Theta, R(theta), P [ Q, QI, C ] LL3, LL2, LL1 on the back face. 

In this website, you may find a good explanation of the use of these scales and the math behind these.

References:

• Robinson, William K: Slide Rules with Hyperbolic Functions. Journal of the Oughtred Society, Volume 14, Number 1, 2005 https://osgalleries.org/journal/displayarticle.cgi?match=14.1%2FV14.1P55.pdf&fbclid=IwAR24M1EPcZGS7rg00MFIHzu5wG8lMXfF2IDdDiu2tQ1Ys1aVL2VctmrOcfw 

• Robinson, Bill: Hyperbolic Slide Rule Archive. https://osgalleries.org/hyperbolic/index.html 

• Following the Rules Info: Hemmi 153 Scales.. https://followingtherules.info/hemmi-153-scales.html