Not all of the forehead surface is appropriate for measurement. Because the distribution of subcutaneous vessels is different from place to place, we recommend the center of the forehead surface for the correct measurement position for iHealth PT3. All of the results measured from other parts of the forehead may not be accurate.
Measurement position: center of the forehead surface
Keep the probe 1.18 in (3cm) away from the forehead. (the optimal distance is about the width of an adult’s index finger).
*credit to Sylvain of iHealth Labs EU
https://helpcenter.ihealthlabs.eu/hc/en-gb/articles/360007203657-iHealth-PT3-Measuring-position-of-the-thermometer