1. This was one of the latest of the Log Log Duplex Decitrig family of rules. An earlier one is the 4081-03 which has similar scale complement. The range was introduced in 1937. The rules were made of celluloid on mahogany. On the earlier rule the mahogany was completely enclosed but on this one the mahogany was arranged so that it formed two visible stripes on the side (see side view below).

2. The arrangement of the scales, with DF, CF, CIF, CI, C and D on one face for rapid multiplication and division on one side and T, SRT, S and D on the other to handle easily many trig problems is slightly unconventional but quite logical.

3. One feature I like on this rule, which I have not noticed as clearly on other rules (though it is probably not unique) is the fact that the cursor hair line and the scale markings are the same thickness. This seems to make accurate alignment much easier.