Definitions:

The pointing model used by comsoft is very simple and incorporates only two parameters: R.A. and Dec encoder offsets. For this reason, when you point SPARO at a source of known R.A. and Dec, you will need to add empirically-derived "SPARO Pointing Offsets" (SPO's) to the actual coordinates or else you will not be pointed at the source.

What does it mean for SPARO to be pointed at a source that has a certain R.A. and Dec? Does it mean that the left beam is pointed at that source? Or the right beam? Or something else? The convetion will be that SPARO is pointed at a position that would put the source half-way between these two beams. So the SPARO pointing offsets are referenced to the "center position" of the chop. So if you want to put the source in your left beam then you have to move the telescope by half-a-chopper throw towards positive R.A. from these "center-position" pointings.

More conventions: Unless otherwise stated, (1) all ASC's, SPO's, and SSC's are precessed to the 2000 Epoch, (2) all SPO's and SSC's refer to pixel 5, and (3) all R.A. SPO's are in degrees of azimuth.

Finally, note that there could be two reasons for non-zero SPO for a give source: (1) the Viper pointing is not perfect, and (2) the source coordinates are wrong. Almost always most of the SPO will be due to the first effect, but for a few sources the coordinates are not precisely known.

The bottom line is that it is the SSC, not the ASC that should be put into the tcl scripts.