MFIT /STEP

          [SIC\]MFIT Y=f(X,&a,...) /STEP A2 B2 ...

    A2  B2  ... are used to pass the unity vectors (steps) for the iteration
    on parameters &A &B (defaulted to 0.1). Poor choice of initial steps may
    lead  to  non convergence. Too small steps will not help converging when
    one starts too far from the solution. Too large steps may lead to incor-
    rect evaluation of the parameter errors. The optimal step for the deter-
    mination of the errors is about the error bar, so  that  all  parameters
    become dimensionless.