This model demonstrates the use of the alternate, percentile parameter formulation. In this case we assume that we have decided to use a Normal distribution to represent the arrival time of someone at work. The use of traditional parameters would require knowledge of the standard deviation of the arrival time, which may be hard to estimate. The use of the alternative parameter formulation allows data to be estimated by others in a more natural way. In the first case, the traditional parameters are used (mean and standard deviation). In the second case, the mean is still used, and the P90 is used in place of the standard deviation, i.e. the time before which the person arrives in 90% of cases. In the second case, the P10 and the P90 is used in place of the standard deviation i.e. the time before which the person arrives in 10% of cases, and in 90% of cases respectively.