a method and apparatus for measuring the rheological properties of a polymer melt includes flowing the polymer melt from a first reactor to a device through a conduit at a predetermined flow rate , measuring a first pressure of the polymer melt at a first location in the conduit , measuring a second pressure at a second location downstream from the first location , measuring a temperature at a third location in the conduit , wherein the third location is between the first location and the second location , and calculating the rheological property of the polymer melt as it flows through the conduit . the method and apparatus do not require diversion of the polymer melt from the main process stream .