Hemmi 2664 (Early Model)

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This 2664 is the earlier model among two of the variants I have. This type had been made between sometime in WWII through sometime in 50's. This particular specimen has "Made in Occupied Japan" inscription, so it is a post-war period production.

It has four trig scales; TI1, TI2, SI2, SI1. TI1 and SI1 are the regular trig scales . They take care of angles down to 6 degrees. In contrast to the most of the trig scale sets which combine Tan and Sin scales smaller than 6 degrees into one scale, this scale set keeps going using separate scales down to 2 degrees where they finally merge into one.

Hemmi managed to squeeze Tan scales for 45 - 70 degrees within the now vacant right half of TI2 scale.

There is another feature to this rule. Take a look at A scale on front. Left hand side is A scale allright, but there is only half of it. The right hand side carries folded L scale.

This makes sense, in the absense of B sacle, only thing you can do with A scale is to read off a square of a number and you do not need a full two cycle log scale to do it. You have DF scale which is folded exactly at mid-point. Similary, one can read off a log of a number using D and DF scales.