Table 1: Number of data pairs, after applying stability criteria to the PMT anode currents and to the trigger rates. Single Pointing (SP), Doubling Pointing (DP), and Single Pointing with Veto (SPV) are explained in the text. The fraction of the data set with a cosmic ray trigger rate below 15 Hz, which we ascribe to seasonal increases in atmospheric extinction, is also listed.

Source	SP	DP	SPV	All pairs	<15 Hz	On hours
Mrk 421	61	44	28	133	20%	38.9
Mrk 501	10	25	-	35	50%	10.3
1ES 1426+428	-	-	33	33	40%	8.8