From Wiki

AcuMath No. 1500 Log Log Decimal Trig

• Type: Log Log Duplex
• Size: 10 Inches
• Material: Vinyl, aluminum brackets
• Scales:
  • Front: LL02 LL03 DF [ CF CIF CI C ] D LL3 LL2
  • Back: LL01 K A [ B T ST S ] D L LL1
• HvH: variant of 8

With vinyl slipcase. LL scales for fractional exponents are marked on the right-hand end of the rule. The CI and CIF scales are also marked, apparently to make room for the legend, "U.S. GOV'T". Clearly manufactured under a special contract.

Look carefully at that legend. It's clear that someone didn't want anyone knowing this rule was government property. They tried to rub it off, to no avail.

The 1500 is a variant on the model 1311. The 1311 was a magnesium-cored rule with black and red markings, the 1500 is layered vinyl with only black markings. Both are described in the 1961 catalog.