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PTINCR is used to set the step size for pointing patterns on the VLBA in arc minutes. A 10-point pattern is used with off, half-power, on, half-power, and off positions in azimuth, and then in the same in elevation. PTINCR gives the offset between the on and the half-power positions. PTOFF gives the distance to the off source positions. Note that the off source positions in elevation are PTOFF arcminutes off in azimuth and two times PTINCR off in elevation. This gives a smooth sequence in elevation which, at low elevation, significantly improves the baseline removal.

Craig Walker 2014-04-14