- MassLynx 4.1 SCN 884
With the mouse, left-click on a peak of interest in the Spectrum window. Then, while still holding the the left mouse button down, drag to the other peak. The mass difference between those two points is displayed in the bottom left-hand corner of the Spectrum window.
As you click and drag between points in the spectrum, a black line appears showing where the start and end points of measurement are. If you're on a peak, the end marker will turn a lighter shade of cyan.