A mask test (or the LabVIEW limit test), draws an upper and lower limt envelope around a waveform. If any part of the acquired signal is outside the envelope, the test will fail. I've had to acquire signals that could not exceed a certain amount of overshoot, undershoot, max/min pulse height, and a few other parameters. Defining a mask allow s all of the parameters to be measured at once. The downside was that it it was difficult to determine exactly which parameter failed. The mask test in scopes or the NI Limit test usually just return the number of points that were outside the limit. There's a shipping example called Limit Testing Measurement.
