[Ian Iveson]

Ken said

I use P-Esq/R where E= peak to peak/2 X .707

That's OK and easier to measure, generally. Won't upset John either. How do
you measure pk-pk voltage?

Note John's comment about phase difference, which doesn't apply if you assume
a pure resistance, as you do in your equation.

Have you measured your winding resistances yet?

cheers, Ian