That's because cells with formulae aren't empty.

Have your formulae return the #N/A error instead - that will be
ignored in the chart. For instance:

   =IF(A1<>0, B1/A1, NA())

You can use conditional formatting to change the font color to the
background color when the cell's value is #N/A if you don't want to
see the errors on your sheet.

Karen -

The cell that contains "" only looks empty to you and me, but Excel sees
the zero-length string.  If you change "" to NA() in your formula, the
cell will now show the #N/A error, which looks ugly, but the chart
interpolates the points on either side of this error.

- Jon
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Jon Peltier, Microsoft Excel MVP
http://www.geocities.com/jonpeltier/Excel/index.html
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