Insert an additional column before the column where you have your
VLOOKUP formula. Suppose that column Y is the column housing those
retrieval formula:

In X2 enter & copy down:

=IF(Y2=0,#N/A,Y2)

Exclude column Y from charts.

flummoxed wrote:
I have a chart, and several series contain data that comes from elsewhere
using a VLOOKUP. However, when the VLOOKUP finds a blank, it returns a zero.
I want the chart to interpolate the data, but Excel charts can only
interpolate blanks, not zeroes. I've used ISBLANK with the VLOOKUP to return
what appears to be a blank, but the chart still sees it as a zero, and thus
will not interpolate. I'd like to know if there's a way to set the value of
a cell to NULL, because "" doesn't work...