A Concise Weights and Measures Conversion Tables Circular Slide Rule. Pat. No 381371. This cool little pocket conversion has a circular slide rule in the center. There is a little card that slides to the left and right that converts length and weight on the front and square and cubic & capacity on the back. It is written in English and has Japanese characters. The whole thing fits in a neat black slide in case. This belonged to my father-in-law who worked in Japan in the 1950\'s and 1960\'s. He worked on early forms of radar and ultimately satellite tracking. This is in very good condition with a couple of hand written words in pencil and of course a few minor surface scrapes from being moved back and forth several dozen times. It comes from a clean, non-smoking home and has been stored in a cool, dry closet for at least the last 30 years. Thanks for looking!

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