The M5200 uses a technique called Sweep Frequency Response Analysis, a proven technique for making accurate and repeatable measurements. As compared to the "Impulse" technique, this technique is the preferred method for making frequency domain measurements. Here's how SFRA works: The M5200 sends an excitation signal into the transformer and measures the returning signals. By comparing this response to baseline and other results (such as from similar units), you can identify deviations and confirm internal mechanical problems.