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 generator to be tested. The closer the distance between the thumb and the air negative generator to be tested, the higher the degree of the tester, and , the smaller the degree of the tester. in order to the accuracy of the measurement results, keep the tester at an appropriate distance from the air negative 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 will 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 each measurement. This negative tester can only measure some household appliances with negative generator, such as negative air purifier, air conditioning fan, air conditioner, etc. which can release more than tens of thousands of high concentration negative oxygen ions. It can not test negative ions released from some ordinary natural environment and some solid ions. The tester is easy to carry and is suitable for testing high concentration sources. Measurement range: 10,000-19,990,000 (/cm³) colour: white Material: plastic Size: 80x30x10mm Package Contents: 1 x Negative Meter Only the above package content, other products are not included. Note: Light and different displays may cause the color of the item in the a little different from the real thing. The measurement allowed error is +/- 1-3cm.