Retired after control failure
The k(L) calculator is no longer a physical recommendation tool
The former calculator extrapolated an eight-point synthetic fit to arbitrary problems. A fresh common-bounds control lowers the line's R^2 from 0.7096 to 0.4370 and fails the optimizer's own linear-pattern criterion.
Archived fit
k = -0.0137 log10(L) + 0.1593
Retained in the Python API for compatibility, with provenance marking it as an unvalidated physical lookup.
Safe use
Choose k as an explicit model or numerical-method parameter, then validate it against a converged reference and report sensitivity. Length alone does not select a calculus.