1. This is a duplex circular rule. The scales on the front face (using where applicable standard nomenclature) are:

• C, as the rule has two cursors, no D scale is needed.
• CI, a reciprocal scale.
• L, logarithms (base 10).
• A, squares with normal decimal markings.
• A, with with binary fractions, that is, against 1.5 on the A scale the number 1 1/2 is marked on the Ab scale (highlight 5 in detailed front view)
• L3, log-log scale from 4 to 1000. The thousands are marked with an M. (highlight 1 in detailed front view)
• L2, log-log scales from 1.14 to 4
• Fractions, in 1/64ths (highlight 4). With two cursors it is possible to add fractional numbers.
• Drill and Thread Scales (highlight 3). The scale from 60 to 1 and on through A to Z   is for drill sizes. To find the size of a numbered or lettered drill you put the cursor over the number or letter and read the size as a decimal on L or as a fraction on the fraction scale. To find the size of drill to use for tapping a perfectly full thread use the Thread Scale. Set the long cursor at 5 on the Log Scale and the short cursor at the number of threads on the Thread Scale (either USS or V form). Turn the long cursor until the short cursor is at the bolt size on the Fraction Scale and the long cursor will give the drill size on the Log, Fraction or Drill Scale, as desired. (Thanks to Bill Kale for the explanation).
• Millimetre to inch conversion (highlight 2)..

2. On the rear it has three scales each for sin and tan covering the ranges 0° - 30° : 30°- 60° : 60° - 90°. (detail back view). It also repeats the fraction scale.

3. The rule has two cursors on the front face, this is an alternative to have two rotating disks as on the Concise and Circulator rules.

4. The first part of a two part article on Gilson rules by Henry Aldinger and Ed Chamberlain appeared in the Journal of the Oughtred Society. Vol. 9, No. 1, Spring 2000.