I don't get how these calculators, or really how people insist that there the true measure of power not a dyno, you would need a dyno to validate the findings of the calculator, since the calculator findings is held in higher regard even so much to call dyno results as wrong there's no way to validate the calculators results, given the fact there's multiple calculators out there given different results and the not knowing how these calculators were formulated and verified it makes no sense to me other than use them as I assume they were intended to be use as a ballpark devise.
i'm guessing that these calculators came about through a large sample of drag cars over the years some with known dyno and weight results others probably most with guesstimation of power to weight and most cars set up well or extremely good getting the most out of less power.