x VariableSpecify the x variable , which indexes the order of observations (or spectra) for binning, detrending, peak-finding, or aligning. For mass spectrometry data, the X variable is typically mz (mass-to-charge ratio) or tof (time-of-flight).To Specify an x Variable:
Left-click a variable from the Available Variables field.
Click to add the selected variable to the X Variable field.