After color inverting the original chromatogram, we count black pixels and thus determine how much of the substance is located at each rectangular area on the film. By using the sliders, you can specify your area of interest. On the left the whole image is shown, whereas on the right your selection is magnified and centered. The percentage refers to the selected fraction of black pixels in that region. The slider for lets you rotate both images and the slider for lets you control the counting tolerance.