AbstractResin uniformity is crucial to the resin supplier and the processor. A new instrument has been developed by Rheometrics, Incorporated to assist the plastics industry. It allows the processors of polymer melts to apply powerful rheological techniques to polymer processing problems on a real‐time basis. The operation of the new Rheometrics On‐Line Rheometer (ROR) is described. The advantages and disadvantages of other approaches to real‐time measurements are given for comparison. Details of some very useful research with polypropylene are disc