STAGES uses the duration of the seminiferous epithelium, in days,
in its computations.  Each animal has associated with it a default
cycle length, given in the literature.  Under certain experimental
conditions, the cycle duration may be altered.

To test for changes in the cycle duration, a new cycle length, in
days, can be entered if so desired.  Continued substitution of
new cycle lengths, until the predicted data match the observed
data, can lead to an estimation of the altered cycle length.