This beautiful device is older than I am and belonged to my late father- in- law who used it for most of his professional life. He bought it whilst at university in the early 1940s.
It is constructed from K&E's special plastic material laminated to a dark wood (probably mahogany) substrate; the cursor is glass. The design carries three patents. It is about a foot long and an inch- and- a- half wide.
The scales on the front are (from top to bottom) L, LL1, DF, CF, CIF, CI, C, D, LL3, and LL2. The CF, CIF, CI, and C scales are carried on the sliding member.
The scales on the back are (from top to bottom) LL0, LL00, A, B, T, ST,
S, D, DI, and K. The B, T, ST, and S scales are carried on the slider.