Previous papers of this symposium have discussed the developments in test methods that have made possible the present uniformity of synthetic rubber produced in Government plants. The paper by W. R. Hucks described the various groups who cooperated with Rubber Reserve in achieving this task. In the present paper we will attempt to give a detailed description of how standardization was achieved both within a plant and among the plants. Perhaps the best way to do this will be to follow the development of the test methods and the standardization of control that led to the uniformity of production with respect to some single property; for example, the ratio of butadiene to styrene bound in the GR-S polymer. In Table I, the average bound styrene content of production from each of sixteen GR-S plants is given for the month of February each year since 1944, together with the corresponding standard deviations since 1945 (the first year the plants analyzed production for this property), which show the variability of production in each plant. It will be observed that the uniformity of production with respect to this property has improved from year to year. The variability of production within each plant has decreased in most instances and the variability from plant to plant has become decidedly smaller. Let us see how this was achieved. At the beginning of the program in 1942 and 1943, there was no test available that was suitable for the control or inspection of bound styrene in GR-S production. The composition of the product in this regard depended upon the ratio of the monomers charged to the reactors and the percentage conversion of these monomers to polymer. The methods for determining the charging ratio and for controlling the polymerization reaction were not sufficiently reliable to assure uniform operations. Consequently, the bound styrene in the product varied from less than 20 to almost 30 per cent, as analyzed at the Bell Telephone Laboratories by an interferometer method. This led to hit-and-miss methods of adjusting the charging ratio from plant to plant near the end of 1943 and beginning of 1944. Obviously a suitable control method and a standardization program in the plants were needed.