I know that RAD is used to expression precision, and I know the formula for it: Per mil RAD = (abs. deviation)/mean X (1000) for parts per thousand. Once you find the relative average deviation--this number in ppt--what is the significance of it? What is it supposed to tell you about the data? What does this number represent?? :uhh: This is probably an elementary topic, but I can't seem to grasp a concrete definition and how it applies to experimental data. Thanks.