OK I follow, AFAIK there's no direct solution to end up displaying "-" for
your zero & -ve values and have the chart ignore them.

Clearly you need the #N/A which you can format to visually appear as a blank
cell, two ways -

Conditional Format:
select the first cell in your list (below assumes it's A1)
Formula Is =ISERROR(A1)
format font to white
copy down (note no $ in the formula)

Custom number format:
[Black]general (change general as required)
Format font in all cells to white

and change your formula to
=IF(B310,CONVERT(B31,"lbm","kg"),#N/A).

Regards,
Peter T

"Duncan A. McRae" wrote in message
ups.com...
Hi Peter, thanks for getting back to me.

In the Options dialogue, it's set to "Plot visible cells only" and
"Plot empty cells as Not Plotted (leave gaps)". In Column C I have the
following formula:

=IF(B310,CONVERT(B31,"lbm","kg"),"-").
or
IF value0 THEN convert value from pounds to kilograms ELSE show
hyphen

Right now, where a "-" exists, the chart is interpreting it as a zero
and dropping lines to the bottom.