I hope that I not borrow, since by sure all can be also read in manuals.
The most simpliest use of inverse LogLog scales together with nomal
LogLog scales are absolute inverse numbers. Absolute, because there is
no need to take care about the decimal point.
If you look e.g. for the inverse of 100 then place your cursor on 100 on
scale LL3 in order to read 10^-2 or 0.01 deending on engravings on scale
LL03. Or 25 on LL3 to read 0.04 on LL03. Just always use the
corresponding scale, so LL1 woth LL01, LL2 with LL02 and LL3 with LL03.
Of course it also works to loo for a number smaller than 1 on an LL0x
scale and read the inverse on LLx.