Hi nicolinux

I did a little google searching, and despite my limited understanding, found the following:

Re: C and D scales, which are logarithmic scales, base 10, and which are the same:

The C and D scales on a sliderule, have a single "Decade", ranging from 1 to 10.
(10 to 90 are also mentioned. but it seems zeros are dropped in some calculations.)
( The watches have divisions between 90 and 10, so a range of 1 to 10 seems appropriate, rather than 1 to 9...)
The "10" at the far right of the C or D scales is shown as another "1".

For a real number x, the distance from the "Start Point" to x is equal to log(x). (distance(x) = log(x).)
The "Start Point" of the C and D scales is the number 1. This is because distance(1) = log(1) = 0.

https://arxiv.org/ftp/arxiv/papers/1706/1706.04390.pdf

log(2) = .30103 (approximately)

log(3) = .47712

- Brian

ps, the link has another link to a virtual sliderule. It has a few subdivisions below 1 and above 10, beyond the traditional ones.
Also shows pips at 1.1 and 1.2, etc, which correspond to logs of 11 and 12, etc, minus 1.