Abstract: A molding system including a mold and a molding machine has been adapted to monitor the position of first and second mold surfaces that move relative to each other to form a mold cavity. The system includes a source of gas under pressure and an orifice on a first molding system surface to direct a flow of pressurized gas from the first molding system surface. A monitoring system monitors the condition of the gas remote from the first molding system surface to indicate the spacing between the first molding system surface and an adjacent second molding system surface as the first and second molding system surfaces move with respect to each other.