Total EOS Longs minus EOS Shorts in order to give you the total outstanding EOS margin debt.
ie: If 5,000,000 EOS has been longed, and 4,000,000 EOS has been shorted, then 5,000,000 has been bought, and 4,000,000 sold, leaving us with 1,000,000 EOS (net) remaining to be sold to give us an overall neutral margin position.
That isn't to say that the net margin position must move towards zero, but it is a sensible reference point, and historical net values may provide useful insights into the current circumstances.
(Anyone know what category this script should be in?)