Possible reasons are as follows: 1) The measurement distance is too far, which may measure the temperature of the surrounding environment. The designed measurement distance of this thermometer is 1-3 cm, and the best measurement distance is about 1 cm; 2) There is a deviation in the measurement position. When taking the temperature, aim the thermometer at the center of the forehead (above the brow) and keep it vertical; 3) Lo may appear when the subject's forehead is covered with hair, sweat or water, has been pasted with fever reducing tape or taken fever reducing medicine, has been blown on the forehead against the air conditioner, or has strong wind blowing on the forehead surface. Please let the subject stand still in a relatively static environment for 5-10 minutes before measurement; 4) there are very few people on the forehead surface temperature is lower than the average person, at this time of the test results were probably "Lo", can put the thermometer to measure "surface temperature" model, and then measure the forehead surface temperature of others, do a contrast, could be determined when the person was normal at this time, mainly focused on the high temperature alarm or fever "Hi"; 5) The parameter of F4- overall temperature offset is wrong.