Doubtfull these are incorrect, this is a rather mature, stable routine, it has been in use for 15+ years.

Issues with manuallyt trying to verify these stiffness values are:

1) Log interpolation of the charts is necessary. The charts are rather course, so any two people likely come back with differing values.

2) If your L/2a ratio is between 1.0 and 1.5, then the software interpolates (linearly) between the two sets of charts.