A platinum resistance bulb thermometer and a fully transistorized switching circuit achieve any controlled temperature within the range of 100? C to 300? C. The accuracy is better than is required by the various national and international test methods. This method of temperature control is much more convenient than the use of separate mercury- in-glass contact thermometers for each different test temperature as used in the Melt Flow Indexer Model No.2. Also, due to the inevitable breakages associated with glass thermometers, the Model No.3 is more economical in the long term, despite its higher initial cost. A mercury-in-glass thermometer, calibrated over a range of +/- 2 C of the test temperature, indicates the controlled temperature. Three of these calibrated thermometers, calibrated either for the same or different temperatures, are supplied with the Model No.3. Unless otherwise requested, these three thermometers will be suitable for o testing at 190? C.