#N/A or NA() is used so that points are not plotted in a line or XY chart,
allowing the gap to be spanned by a line. Since no marker is drawn, there
are no data labels which my show #N/A. In other chart types, #N/A is
interpreted as a zero value, so a bar is present but not generally visible
because of the zero value, but a data label may be present to show #N/A. For
these charts, it is better for the source data to contain "" rather than
#N/A. If you haven't gamed the source data to try hiding points, game it
like this to hide a failed lookup:
=IF(ISNA(<lookup>),"",<lookup>)
- Jon
