Measurements of the length and height of a total of 2320 genuine signatures from eight individuals have been collected. The signatures for each of the individuals were written, during normal 'course of business', over an appreciable period of time. For five of the individuals, the data are such that it is possible to consider them in monthly batches, while for the other three they are considered in daily batches. A study of the variation with time has been considered and, in nearly every case, the between-batch variation is statistically highly significant. The results are summarised in graphical form an a tentative first principle of handwriting variation is offered. (Publisher abstract)