means an employee who is engaged in operating, including starting or stopping, self-propelled or stationary plant by employing the mechanisms and controls of such plant to perform the functions for which it was designed or adapted, who checks, scrutinises or regulates the running of and the work done by such plant and who may make running adjustments and minor repairs to such plant or perform the daily maintenance of such plant; and in the case of self-propelled plant "operating" includes the driving of such plant, and for the purpose of this definition "operating" includes all periods during which the operator is obliged to remain at his or her post in readiness to operate such plant.