Visual guide to the usage of a PIT. In case the estimated PDFs are to broad with respect to the position of the true value, a convex histogram with a peak in the center can be observed (a). As soon as the predicted densities are too narrow, the evaluation of the CDF at the true redshift exhibits in most cases just very low and very high values. Therefore a concave, U-shaped histogram will be produced (c). Only in the case where the widths of the predicted densities is in accordance with the deviations from the true measurements, a uniformly distributed histogram is generated (b). This indicates sharp and well calibrated predictions.