 The three values chosen for friction loss correspond to, in US units inch water column per 100 feet, 0.01, .03, and 0.1.Note that, in approximation, for a given value of flow volume, a step up in duct size (say from 100mm to 120mm) will reduce the friction loss by a factor of 3.Note that, for the chart and table presented here, flow is in the turbulent, smooth pipe domain, with R* < 5 in all cases.