Turn on the power and let the air pump continually work for 15 minutes. Put empty sample tube on the test base, turn clockwise the clamp assembly control to press the tube tightly on the test base, now the manometer level rises and approaches the red spot in the outside manometer, if the level is lower, input some water by the glass tube supplied, if higher, draw from the pressure constant regulator some water until the level coincides the red spot. Please note that do not do it by adjusting the manometer level control. The red mark on the regulator is a reference mark before connecting the power, above procedure is the right procedure.