I use the enlarging dial in my Kodak Darkroom Data Guide. There is no math calculations involved. A ruler is the only other tool involved. Very simple. There is also a exp correction for using polycontrast filters. Since Kodak seems to be turing it's back on us, they probably don't publish them now(would be nice to be wrong). If you can at least look at a copy, you could make a chart for future reference. If I didn't have a Kodak Data Guide, I'd do the math and make a chart.