a method and an apparatus for monitoring the process stability of an injection molding machine having a reciprocating screw engaged in the plasticating of a moldable material in preparation to its being introduced into the mold cavity . the invention involves the measurement of the duration of the operation of the screw engaged in the plasticating of the moldable material and includes the analysis of this duration over a period of time thus providing the supervisor with the necessary information to determine whether the machine / process is meeting or deviating from the desired operating requirements .