BI Scale
An inverted B scale. Numbers increase to the left.
BI is found on some slide rules, but certainly not all. We're not going to delve into extensive tutorials because to be honest we can't think anything useful. But here's some things it might have been used for:
 problems involving inversesquare laws.
 to find y = 1/x^2 : set cursor at xC, read y on BI.
 This is useless however, since you can do better: y = k/x^2, in one step, using just A,B,and C.
 chained multiplication using A,B and BI
 identical to chained multiplication using D,C and CI, but with extra error!
 reading secants, cosecants, and cotangents when trig scales refer to A,B.
 But our trig scales refer to C and D, so not too useful here.
Please write in if you know of common, useful calculations that can be done especially efficiently with a BI scale, and we'll put them up here.
We don't include an "AI" counterpart, although it appeared infrequently on other slide rules. If you want an AI scale, just put a BI on the stock.
