e = d^a

d = e^(1/a)

It is equivalent to taking the a-th root of e. For example e^(1/2) is the square root of e. I hope that clears it up. There are lots of reference pages on the internet that might help refresh your memory of powers and roots. Don't be too ashamed, every now and then I forget some maths and end up kicking myself!

lh

thx.