Thanks, I see when I thinned the lines down to zero and brought the
Excel markers back that they now pass closer to the centre of the marker
than they did before.

Yes, I found it was better when I used a size that was either an exact
multiple of the final size, or the exact size. But it still freaked me
out when I found out that drawing objects weren't staying where I put
them. I had hoped to create little bit maps or Autoshapes of triangles,
arrows, and vertical and horizontal lines, to expand the repertoire of
point markers available in Excel, but I wasn't confident that the
results I got would not give the wrong values if I tried to use them to
show scatter data.

For really fine lines that go exactly where they're needed, I find I
can't beat the ubiqitous error bar. This is an example of my using them
to create an Edward Tufte style "dot dash plot":

  http://www.branta.demon.co.uk/science/dels-dot-dash-demo.xls

This is something I was discussing a while back with Jon Peltier, and I
eventually implemented it using his and Tushar Mehta's tutorials on
dummy ranges for axes for inspiration.

(*This* is the sort of thing I would like to see in a new version of
Excel, not metallic surface effects)