Some infrared thermometers come with lasers to help gauge the size, or location, of the area being measured. And because the location of the lasers, relative to the area being measured, can vary by unit, it might take a little extra training before they can be used effectively.
For the most part, infrared thermometers (with laser guides) can be divided into two groups: those with single lasers and those with multiple (two or more) lasers.
Single laser units can be particularly helpful when taking measurements from far away. They assist with aim, and control, more precisely, the location being measured. However, depending on the infrared thermometer, the laser may indicate the top, center, middle or sides of the circle of surface area being measured.
It’s also possible that the position of the laser point, relative to the circle of measurement, will change depending on the distance from the target – this is referred to as optical range. Consult the user guide for more information about laser placement and optical range.
Infrared thermometers with multiple lasers typically offer a better indication of the diameter of the circle of surface being measured. Even infrared thermometers with very small spot sizes and low DTRs are able to use multiple lasers to great effect. (See the ThermoWorks Close Focus Infrared Thermometer whose two lasers converge at the point of optimal distance from the target.)
Check the user guide for information about the effect optical range has on the performance of the laser indicators. Indicators can frequently cross each other and be affected when specified distances from the IR gun are reached.
source : www.thermoworks.com