Hi simplex,

Appreciate your formula, however I'd like to say this is not the general equation, because delta only equals to 19 in this specific case, and the 20 is not derived from delta + 1, its origin is from the same book page 13, that 20 is a constant in this equation, if the delta changes your formula could be wrong.

the correct equation should be K = 10^(-3/(20*(longP-shortP))

no offence, just want to help