Tools - Options - Chart - Plot empty cells as: Not plotted (leave gaps) works
only when the cell is actually empty. The cell is empty when raw data is
missing, but the raw data has to be subtracted from a constant value. I'm
using =IF(ISNUMBER(B4), B$1-B4,NA()) which returns #N/A when B4 is blank.
The cell is not empty and consequently is plotted as an interpolated value
between B3 and B5.

I've tried copying and pasting values only and using "" instead of NA() to
no avail.

Short of clearing the contents manually (5% missing data points scattered
throughout 25,000 values) is there another way to leave gaps in the line
chart?