How to tell excel to ignore #NUM! errors in plotting a line chart?

You can setup a graph to handle missing data, but not to handle faultive data.

So, to solve this you should protect your time-series with a code like:


Whereby A1 would be your "raw" data and B1 is the cell/column which you will have to use as chart-input.

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Consider using =IFERROR(A1,NA()). This will replace all error values with NA(), which Excel will automatically skip giving you a gap.