1. This is one of the rare rules to have hyperbolic functions (sinh and tanh).
2. On a "normal" rule these can be calculated using the log-log scales by the following relationships:

    Sinh x= (e^x - e^-x) / 2
    Cosh x = (e^x + e^-x) / 2
    Tanh x= (e^x - e^-x) / (e^x + e^-x) = Sinh x / Cosh x

Clearly where there is a need for these functions special scales can both minimise the amount of calculation and reduce the chance of errors.