In Pyrocat HD, 2.5g of metol replaces .2g of phenidone - or 25g metol replaces 2g phenidone. Based on that, I mixed some Pyrotriethanolamine, which calls for 18g of metol, with 2g of phenidone. My scales only measure whole grams - not fractions. The developer works fine. I'd guess you'd be close using the 2g=25g calculation.
juan