After you toggle the "CompSrc" button on, the NSHARP Skew-T and hodograph displays compare all active sources at the current time for the current station. This can be handy to overlay model data forecasts at particular times. The name of the source in the source table is color coded to match the colors of the Skew-T and hodograph traces.
The left/right arrow keys step through time. The up/down arrow keys cycle through stations. The shift + up/down arrow keys cycle through sources.
Point A model forecast SkewT and hodograph plots for GFS212 (red) and ETA218 (green).
Toggling the filtering off for some sources in the inventory table on the upper right part of the display can help manage large numbers of soundings in compare source mode.