See Rupesh's spot++ posts.
Basic conclusion is that we are fairly well centered in x (and in y). We found definitively the wall in x by moving symmetrically (4mm) to either side. The y position scans are less definitive because we don't see a spike at one side--indicating wall, but a slope (across the raster current scan ) which increases as we move closer to the "wall". However, since these targets have vertical flow, the "walls" in y are not well defined (they are not like the walls in x)...so perhaps we should not expect to see a wall spike as in x...experts should comment here.
Can we determine the true/effective raster size from this study?
Assuming we are centered on the target in x and knowing that we hit the
wall with a 4mm excursion to either side implies that the raster size
with tails is no smaller than 16 mm in x (assuming 20mm cell width).
Assuming the same blowup ratio (16/11) for y gives (8.5*16/11) 12.4 mm.
So the effective raster size is 16 by 12.4 mm (pretty big).
A copy of this log entry has been emailed to: paschke@jlab.org, rom@jlab.org, dalton@jlab.org,silwal@jlab.org