This product is a 695 thermometer and hygrometer: the temperature error between plus and minus is about 1-2 degrees Celsius. Humidity 50%--70% error is plus or minus 5%, 30%-50% error is plus or minus 8%. The thermal sensor is located at the vent. The sensitivity is very high. A slight temperature difference in the surrounding environment will change the temperature. This product is for healthy living and cannot be used as a measuring tool. An error of 1-2 degrees is normal. It is recommended that after receiving the product, you place all thermometers in the same room (away from windows, air conditioners, humidifiers and other household appliances, which can affect the readings) and let them sit for 24 hours (this will reset the sensor after shipping) and recheck the readings so that the data will be more accurate.