1. Turn the switch to ON gear 2. Keep the thumb in contact with the square metal sheet of the front panel. The metal sheet on the back the air negative ion generator to be tested. The closer the distance between the thumb and the air negative ion generator to be tested, the higher the degree of the tester, and vice , the smaller the degree of the tester. in order to the accuracy of the measurement results, please keep the tester at an appropriate distance from the air negative ion generator to be tested. 3.Do not Contact the square metal sheet on the back of the tester with your hands during the measurement. Otherwise, the degree be inaccurate. 4. There is no sign in front of the degree shown. Indicates that positive ions are measured; if "-" is displayed, negative ions are expressed. 5. Keep the machine switch in "off" position before each measurement. This negative ion tester can only measure some household appliances with negative ion generator, such as negative ion air purifier,