Putting limits (absolute bounds) on the allowed values for a given parameter, causes Minuit to make a non-linear transformation of its own internal parameter values to obtain the (external) parameter values passed to FCN. To understand the adverse effects of limits, see ``The Transformation for Parameters with Limits'' in Chapter 1. Basically, the use of limits should be avoided unless needed to keep the parameter inside a desired range.
If parameter limits are needed, in spite of the effects described in Chapter One, then the user should be aware of the following techniques to alleviate problems caused by limits: