Levelness is ratio of inclination of found results. When a found result is horizontal to offset frame, "100.0" is output. When it inclines at 90.0 degrees, "0.0" is output. The probability of succeeding in picking is generally higher when levelness is bigger.
Check [Threshold], enter the threshold in the text box, and a found result with a smaller threshold than the levelness is discarded. When [Measurement] is selected from the drop-down box of the [Output], levelness is output to selected measurement.
There are tools in the command tools such as the 3D Peak Locator Tool that do not calculate inclination. For such tools, levelness of found results is always output as 100.0.