A model is.proposed for the systematic arrangement of work element times. This model consists of a grouping of all work element times along the time co-ordinate either in groups of equal size or with the time span of each group increasing with the mean time of each group. The statistical properties in analysing work by means of data thus arranged are investigated. A comparison is madewith the sampling error.of.such,data, the observational error, when the error consists of referring the work elements to the wrong group, and the natural variation of the performance time.