Shadow gradient is crucial for the perception of quality. That's why the fractional gradient method, based off the results from the first excellent print test, uses a gradient of the shadow that is proportionate to the overall gradient. Film speed is arbitrary if it doesn't have a direct connection to the characteristics of the film. The ISO speed standard is linked to the fractional gradient method through the use of the Delta-X Criterion. When the contrast parameters of the ISO standard are followed, there is a known and consistent shadow gradient 0.29 log-H units from the 0.10 fixed density independent of curve shape. This is how we are able to make practical comparisons of speed between different film types and to assign film speeds with relevance. The ability for the film to reproduce luminance differences of the subject is what determines quality. A fixed point of density as Jones writes, "has no significance as an indication of the ability of the photographic material...except insofar as it may have some bearing on the exposure time required to make a print from the negative."