scope:

This method is designed to measure the weighted average fiber length of a pulp. If a fiber is 1 mm in length and weighs w mg, then for a given pulp, the weighted average length (L) is Σ(wl)/Σw, or the sum of the products of the weight times the length of each fiber divided by the total weight of the fibers in the specimen.

Use of either Clark type or Bauer-McNett type classifier will produce identical results within the stated precision.

Fiber length may also be measured by TAPPI T 271 "Fiber Length of Pulp and Paper by Automated Polarized Optical Analyzer Using Polarized Light." The results may not agree as the measurement methods are not the same.