From Trace (Limit Tests Dialog Box)

A limit test can be recreated from a recalled trace that had a limit test applied. When trace data is saved, if that trace had a limit test applied, the limit lines are saved as part of the trace data. To use the limit test again, it must be recreated. When the limit test is recreated, all limit lines (with their names and parameters) are recreated point for point. The limit test can then be edited and applied to new data.

is inactive unless a trace has been recalled.