How to suppress the display of zero values in a data series?

Hi All,

I have a chart with three data series, 2 series have 52 (weekly data) values each & the 3rd series has between 1 & 52 data values (building up from 1 to 52 over the course of a year).

If I manually add data values to the data underlying the 3rd series the corresponding chart line increases however if I use a formula to reference whether or not data values should be added (returning a "" if no data is yet required) the data series intreprets this as a zero & shows it as such. If the data cell is blank (no formula) then it is not shown in the data series, which is the effect I need to achieve.

This is Excel 2007 charting & I would be extremely grateful for a pointer as I'm pulling my hair out here[/SIZE][/COLOR][/FONT] . Thank you in advance, enq.