text: The most widely used numerical laser diffraction results are: 
  * The median volume-weighted diameter, or D. Derived from the cumulative curve, it represents the particle diameter separating the upper 50 % of the data from the lower 50 %. 
  * The D and D values, also derived from the cumulative curve. 
  * The mean volume-weighted diameter, also termed D[4,3] or De Brouckere mean diameter.
  * The span, which gives a measure of the width of the particle size distribution, and is calculated as span = [D – D]/D.