I am plotting an XY scatter. The X and Y data is found in cells that have
formulas in them, and the result of these formulas changes based on user
input via a drop down box. When the first cell in the range is a blank (not
zero, the formula returns "", i.e. an absence of data), the chart changes
format such that the Y values are plotted against a series 1,2,3,.... etc.
If the blanks fall elsewhere in the columns, the plot is charted
appropriately. I cannot substitute the blank with a zero, because it changes
the nature of the plot and the regression line on it.

Thank you for your assistance.