Yes, that's an ironmonger's rule, with special tables to work out the capacity of boilers and something else where the weight, in hundredweight, CWT, corresponds to the price, in Pounds, shillings and pence, LSD.
Quite specialist and rare, I think, and in very good condition.
I know that there is an inner world within tool collecting where well informed specialists pay quite high prices for these beautifully made antiques. I'm not a rule collector. Do we have any on here?