314L+ does the binning start from the left or the right side of the CCD?

[Dave92F1]

When I do 3x3 binning on my 314L+ I get a 463x346 pixel image.

The full resolution image (no binning) is 1389x1039.  Since 346 * 3 = 1038, this implies that one column of pixels isn't used when binning 3x3.

Which one?  The leftmost column or the rightmost one?

I'm trying to align an unbinned image with a scaled-up 3x3 binning image; to do that accurately I need to know whether to align it on the left or on the right...