J.Hemmi-Sun Electro 81 with Decimal Keeper

The Model 81 Electro was manufactured by J.Hemmi-Sun Co. in Japan in the period 1919-1942. Fabricated with Bamboo parts coated with white celluloid, assembled with a metallic strip, and engraved railroad style scales. Model 81 was a clone of the A.W Faber 378 Electro, produced in the same period of time. During the production time, Model 81 had some little variations mainly in the scales and cursor . The models produced before 1932, had the scale set: Front Face: Upper edge - 27cm ruler // LL2, A(KW) [ B(HP), C ] D, LL03 || Lower edge - 10in ruler, and on the slider's back face: [ S, L, T]. There are also interior scales that you can see when shifting the slider: Motor TL=%, Volt . Models produced after 1932 have an extra scale CI between scales B and C on the slider. The other variation was on the rule's cursor; this may be simple metallic framed, or extended with a useful (and nice) decimal keeper arrow.

This rule, as the its name indicates, was designed for electrical and mechanical engineers, but having an interesting difference with other engineering slide rules, the lack of the standard K scale used for cube-cubic roots calculations. In model 81 and similar, these powers-roots, and other fractional powers are calculated with the two Log-Log scales. Additionally, Model 81 interior scales allow to find, with one setting of the rule, dynamos and electrical motors performance knowing their power, as well as the loss of tension in cooper electrical lines for alternate or continuous currents, given length and cross section.

Based in the type of cursor and scale set, I assume that the rule in this collection was fabricated, according with Paul Ross documentation, in the 1928-1932 period:

Click on the next link to see professional panoramic pictures of the Model 81 Electro:

https://www.sliderulemuseum.com/Hemmi/Hemmi_Electro_Pre1927_TrainTrackScales.jpg

https://www.sliderulemuseum.com/Hemmi/Hemmi_Electro_withDecimalKeeper_DonatedByJiroHiguchi.jpg

Here are extra images from Paul Ross, The Slide Rule Trading Co. Hemmi Slide Rule Catalogue Raisonné Web Page. These correspond more to the model in this collection:

http://srtco.us/HemmiCatalogueRaisonne/HCR_Pics/4.jpg

References:

• Ross, Paul: A Comprehensive Hemmi Slide Rule Catalog. Journal of the Oughtred Society. Volume 12, No. 1, Fall 2003: https://osgalleries.org/journal/pdf_files/12.1/V12.1P41.pdf

• Ross, Paul: The Slide Rule Trading Co. Hemmi Slide Rule Catalogue Raisonné : http://srtco.us/HemmiCatalogueRaisonne/Index.htm

• Ross, Paul: The Slide Rule Trading Co. Hemmi Slide Rule Catalogue Raisonné :Part II: http://srtco.us/HemmiCat2/Index.htm

• Chamberlain, Edwin: Slide Rule Decimal Point Location Methods. The Journal of the Oughtred Society. Vol. 7, 1 Spring 1998. http://www.oughtred.org/jos/articles/V7.1_Chamberlain_Decimals.pdf