Calibration Light helps you to find a uniform illumination of your work surface. On the left side, the work area is divided into several panels, moving the camera or the light source, the ideal condition is achieved when all the squares are colored green. In the case these are yellow or worse red means that area is in proportion far from the ideal average value.
On the right side an image histogram acts as a graphical representation of the tonal distribution in your image. It plots the number of pixels for each tonal value. By looking at the histogram you will be able to judge the entire tonal distribution at a glance.The ideal condition is realized as all the points are concentrated in the average value (medium gray) in a very narrow Gaussian. Slider at the bottom can help you find the right exposure.