A technique for interpreting measurements of fiber length distribution is demonstrated on cotton samples taken before and after a single mechanical processing stage. Theoretical methods are used to relate the observed change in length distribution to the fundamental nature of the breakage mechanism inherent in the process. This technique is demonstrated with length data derived from the Peyer Fibroliner/Almeter (FL-IOI/AL-101) instrument system.Because of the recursive nature of fiber breakage processes, there is a degeneracy in the possible solutions. An objective mathematical criterion was constructed by which the "best fit" of the data to the theoretical possibilities can be used to identify the correct solution. It is also possible to characterize the fiber output state by comparison to an "ideal" or standard distribution, rather than the actual input distribution. In that case, only one experimental measurement is needed, and the state of the length distribution can thus be determined from a single sample at any stage in processing. The accumulation of damage to a cotton can be tracked through sequential stages of processing. Since high-volume instruments (HVI) for classing cotton already contain capabilities for length distribution sensing and information processing, there may be applications of this technique for obtaining maximum use from fiber length data obtained during instrument grading of cotton.