Why do we use equivalent spherical diameter?

For perfect spheres, diameter can be used as a measure to describe their size. Real-world particles are characterized by their irregularities, resulting in several different size descriptions that could validly be used but with some difficulty. The equivalent spherical diameter was introduced as a valid base with which results from different techniques could be harmonized to facilitate and unify the illustration. The D shown below is the equivalent spherical diameter, which is not the largest or smallest diameter measured when interacting with the laser but can be the average of the sum of all that particle’s orientations towards the laser.

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