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Lawrence Engineering Service No. 10-B

• Type: Closed Body Mannheim (would be "enhanced", but no trig scales)
• Size: 10 Inches
• Material: Boxwood
• Scales:
  • Front: A [ B CI C ] D K
• HvH: copy 1: 1570; copy 2: 1571

With heavy paper wrapper. The rule is apparently unused, very clean and white, the slide almost stuck from having swollen in place while sitting in 50 years of humid weather. There are no scales on the back of the slide. The runner shows some oxidation.

The Lawrence Engineering Service of Peru, Indiana, proudly presents their model 10-B boxwood slide rule. Near as I can determine, Lawrence made these beginning in about 1939. In a 2 month period, I've personally seen 3 of these, was offered two more, and seen 4 up for auction. So, I guess every growing boy should have one. Or by this time, every growing boy's grandfather...

The reverse is notable. This relates unit conversions in terms of integer proportions to be set on the slide. I'd say this was unique, but see the Scientific Instruments Relay 105. The reverse of that rule has a bit of film with a reduced copy of the reverse of this rule on it.

Rule #1 kindly provided by Ian Johnston.

A second rule came to me recently. The runner has a magnifying feature and the reverse varies from rule #1. It came in a badly delapidated paperboard box, not pictured.