All computations in the LISST-100 are based on the assumption of the particles being spheres. Although there is a wide body of literature in the optical sciences that deals with regular and (recently) irregularly shaped particles, it is of no generalized value. A future Application Note will address this issue in more detail. However, note that the measured scattering, being principally the light diffracted around particles, responds to particle cross-section. Spheres being the lowest cross-section per unit volume whenever non-spherical particles are examined, the volume concentration will be overestimated. The fractional overestimate depends on the shape itself; thus, there may be academic interest in estimating this ‘overestimation ratio’ for selected natural/man-made particles. UPDATE September 2008: Sequoia has published original research on this topic, please go to the Technical Papers section in our library and download this paper: Agrawal YC, Whitmire A, Mikkelsen OA, Pottsmith HC (2008): Light scattering by random shaped particles and consequences on measuring suspended sediments by laser diffraction. Journal of Geophysical Research 113, C04023.