Two settings and one geometry account for nearly every disagreement.
Emissivity
If one instrument is fixed at 0.95 and the other is set to 0.3 for bare metal, they will disagree substantially — and the second one is right. Emissivity is a property of the surface, and an instrument set wrongly reports a temperature that is not the surface’s.
Distance
At 12:1, one instrument held at 30 cm (11.8 in) measures a 2.5 cm (1 in) spot and another at 1 m (3 ft) measures an 8 cm (3.1 in) spot. If the target is small and hot, the closer instrument reads higher and both are averaging correctly over different areas.
Angle and reflection
Shiny surfaces reflect. Two instruments at different angles see different reflected sources — a window, a light, a person — and report different values.
What to do
Match the emissivity setting, get both to the same distance, and measure a matt surface or a patch of matt tape. Under those conditions they should agree within their stated tolerances, and only one of the thermometers we compare publishes one.
This does not replace the manufacturer's instructions. Every accuracy figure, measurement category, laser class and detection depth on this page is reported from the manufacturer's own documentation and named as such — none of it is calculated here. Working near a live installation, and trusting a detector before drilling, are safety matters: follow the figures printed on your own instrument and in its manual, which take precedence over anything on this site, and where a job belongs to a qualified person, hand it to one.
What gets asked here
Which reading should I believe?
The one taken closer, on a matt surface, with a correct emissivity. If none of those conditions is met, neither.
Do contact thermometers avoid this?
They avoid the emissivity problem entirely, because they measure by conduction rather than radiation. They need contact and time to settle.
Last reviewed 31 August 2026