To help you find correct emissivity setting for your infrared thermometer, ETI provide an Emissivity Table with the emissivity rating of many common materials listed. For measurements of many materials, inputting the right emissivity value is as easy as checking the chart.
Chart values, however, are just estimates. The actual emissivity of a surface you're trying to measure will vary slightly depending upon its color, thickness and even its temperature. Verifying the precise accuracy of an infrared measurement can take a little more planning.
This is particularly true when your infrared thermometer is set to lower emissivity values. Since materials with low emissivity are poor emitters of infrared energy by definition, infrared thermometers amplify the infrared radiation levels they detect when they perform their calculations. This can lead to the magnification of slight errors and make temperature measurements at lower settings seem erratic.
There are two ways to handle this: