1. Check that the thermometer lens is perfectly clean. If in doubt, clean with a cotton swab slightly moistened with alcohol. After cleaning, wait 30 minutes before taking a new measurement.
2. Check that there is no hair, sweat, cream or any other cosmetic product on the forehead surface.
3. Make sure the thermometer is at the same ambient temperature as the person who is taking the measurement for at least 30 minutes.
If in doubt, check the temperature with a standard thermometer and / or consult a doctor.