The DIMM is a widely accepted and often used instrument for seeing measurements. Nevertheless, its incorrect use may give rise to errors in seeing values. A detailed analysis of the parameters involved in the seeing calculation is being undertaken and the effect of saturation of the spots in particular is analyzed in this contribution. Our results reveal that the saturation increases not only the photon noise but also the speckles, which will acquire a greater relative weight with respect to the stellar spot. The result is an increase in the variance of the centroids, which results in artifically higher seeing values.