The absolute rates for mass-changing processes such as NP sublimation, etching, or growth are simply the slopes of M vs. time in units of Da/second. Slopes are determined by fitting ranges of M vs. time for which the slopes are roughly constant, and the fitting process averages out most of the effects of the ~0.2% scatter in the F z (and M) measurements. The absolute accuracy of the slopes, thus, depends mostly on the absolute mass accuracy, i.e., the uncertainties in absolute rates are typically in the 1.5 % to 3 % range, depending on whether Q initial is small enough for exact determination or not. The absolute mass uncertainty primarily affects the absolute mass scale, i.e., comparisons of kinetics under different reaction conditions or changes in kinetics over time are unaffected, to a reasonable approximation.