` :::If j = log10(b) then b =&nbsp10j.;   ::::1 ha =&nbsp104; m² :::So for the hectare j =&nbsp4.;  For the square mile it's not so easy to figure out: you'd need a table of logarithms, a (decent) calculator, to be really good at arithmatic or a computer.  I stick ``1609.344`` in A1 and ``=log(A1)`` in B1 in Excel.  A1 is b & B1 is j. p `