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Keuffel and Esser Model 68-1100 Deci-Lon

• Type: Log Log Duplex
• Size: 10 Inches / 25 cm
• Material: Plastic, aluminum brackets
• Scales:
  • Front: Sq1 Sq2 DF [ CF CIF L CI C ] D Ln0 Ln1 Ln2 Ln3
  • Back: Ln-3 Ln-2 Ln-1 Ln-0 A [ B T SRT S C ] D DI K
• HvH: 4468

"Deci" referred to the use of decimal fractions, rather than arc minutes, to divide the degree on the trig scales. "Lon" refers to the eight natural logarithm (Ln) scales for log-log-based exponential calculations. The Deci-Lon's added log-log scales increased the range to e-10 = 0.000045 through e-0.001 = 0.999 and e0.001 = 1.001 through e10 = 22000. The catalog from 1962 states that the material used was "shatterproof synthetic." Some claim this is Ivorite, but there are other rules in the same catalog that state they're made from Ivorite. This rule almost feels like nylon, but the slide isn't at all sticky. Perhaps a vinyl.

This was K&E's top-of-the-line rule until they got out of the slide rule business, and can be considered an expansion of the 4081 Series, including 4081, 9081 and 68-1251.

The serial number, 025787, suggests a manufacture date in 1962.