A method for correcting an offset for a pressure difference measured using a differential pressure sensor situated in an air duct. The apparatus includes a phase detector having a first and a second input. The elongate molds are thereafter driven through first and second resinfiberglass application stations to apply a composite of resin and fiberglass strands. The AD conversion correction coefficient for the digital correction unit is calculated on the basis of the digital correction result of the digital correction unit in the first period, and the digital correction result of the digital correction unit in the second period. The method includes detecting a dimming characteristic in an energy source that provides energy to be transferred to a load via a magnetic component, receiving a dimming control signal, and controlling a switch in connection with the magnetic component based on the dimming characteristic and the dimming control signal to transfer energy to the load via the magnetic component. Hydraulic pressure control during automatic brake control is carried out by the first and second proportional solenoid valves.