Graph paper scaled so that the cumulative distribution function for a specified probability distribution makes a line. This then provides an informal test as to whether data might reasonably be supposed to come from that family of distributions, by considering how closely the observed data fit some line. If it is a satisfactory fit, it can also provide estimates of parameter values. The most commonly tested distribution is the normal, so this is the most common probability paper, often generated now within a statistical computer package while testing assumptions for sophisticated procedures.