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 faces 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 versa, the smaller the degree of the tester.in order to ensure 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 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 before each measurement.This negative ion tester can only measure some household appliances with negative ion generator, such as negative ion 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 ion sources.Measurement range: 10,000-19,990,000 (ion/cm) colour: white Material: plastic Size: 80x30x10mm Package Contents: 1 x Negative Ion 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 picture a little different from the real thing.The measurement allowed error is +/- 1-3cm.