Hemmi War-time Economy Rule

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This rule is believed to have been used in military schools in WWII time.
The bottom scale in front is combination of A and L scales. Left half is half A, and right half is folded L scale. How do you use them? Use D and DF to read off squares and log values. Folding at sqrt(10) comes handy.

There is another neat idea built into the trig scales. For some reason, this rule has separate Sin and Tan scales below 6 degrees. However, TI2 scale extends only down to 2 degrees. You will use SI2 scale from there. The difference between Tan and Sin is small enough

The remaining TI2 space is graduated with Tan 45 - 70 degrees. Another space saving idea.

Click here for Full Image of Trig Scales