Being able to measure film density makes calibrating exposure and development fairly easy. Densitometers, unfortunately, cost around $800 and most photographers have better uses for that much money.(posted 8395 days ago)Federal regulations require hospitals and radiology centers that perform mammograms to have a rigorous quality control process that includes densitometry readings of the x-ray films, so they all have densitometers.
If you know anyone who works in a radiology department you may be able to bum a few minutes with the densitometer. (I found that a dozen bagels and some cream cheese smooths the process.)