Particle testing data calculation is generally divided into 2 methods, Unconstrained fitting inversion and  constrained inversion fitting  inversion.

Constrained fitting inversion before calculation assumes that the particles meet certain distribution, then get inversion of particle size distribution

based on the inversion rule. This operation is relatively simple, But because of unavoidable deviation between prior assumptions and the actual

situation, thus the test data caculated by constrained fit method does not reflect the actual size distribution of the particles.

Unconstrained fitting Inverse method makes no assumptions on the particles before test, directly and accurately calculate the particle size distribution

by light intensity.  So this method will get more realistic and reliable particle size distribution data, are more valuable for R & D.

Preconditions of the calculation is reasonable detector design and size grading, which have higher and serious requirement for equipment quality.