Abstract: Apparatus for controlling the operation of an injection moulding or extrusion tool comprises in this specific case of an injection moulding machine: means for measuring and displaying the numerical values of the temperature at the or each injection nozzles location at any given time; means for measuring and displaying the numerical values of the electrical power consumption of the or each mould cavity at any given time; means for controlling the temperature of the or each mould and/or the or each platen and/or the or each manifold and/or the or each seal of the tool in response to variations in the magnitude or rate of change of the electrical power consumption of the or each mould cavity.