Title: Comment on ``Source of error in foil thickness calibration by x-ray transmission''
Abstract: A recent paper by Boster showed that the x-ray transmission through a nonuniform foil is greater than that through a uniform foil that has the same area, weight, and density. Through examples, it was demonstrated that the ratio of the transmission in the two cases is independent of the foil thickness. It was claimed that the percent error in the average foil thickness as determined by x-ray transmission is related directly to this ratio and thus also independent of the foil thickness. It is shown in this note that the error in the average foil thickness depends on the natural logarithm of this ratio, and the percent error is inversely proportional to the average foil thickness.