The simplest solution works for me:

But if you want to calculate a logarithm to a arbitrary base (jit.op @op log is just a natural logarithm) you can use this formula: log(x)/log(base). (see https://en.wikipedia.org/wiki/Logarithm#Change_of_base)

Thanks a lot KLSDIZ

All I need to know (or at least this is what I understand) is that log is a function and so it needs the () as in log()

so vexpr log($f1)/log(64) + 1. or vexpr log($f1)/log($f2) + 1 would give me the dynamic base.

Thanks

what I actually wanted was a booster in both directions not even a log.

here it is