The industry standard approach for measuring grind size distribution is to use a laser diffractometer. These machines cost hundreds of thousands of dollars, and so they are inaccessible to most coffee roasteries. These machines produce highly replicable results, and they have long been considered the ‘gold standard’ for measuring grind size distributions.
In this video, Matt explains how the machines work
However, as well as being out of reach for all but the largest roasteries and equipment manufacturers, the way these machines work is something of a ‘black box’,