I have tried this with my actual data, and everything works smoothly,
including the monotonically decreasing error rates. e.g.:

                               formula          Error
1                                   Cr           0.41666667
2                              Cr + Mg       0.16666667
3                         Cr + Mg + Al     0.04166667
4                   Cr + Mg + Al + Ba   0.00000000

Thank you for your help.

Ty Smith

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