Badunit,
This is interesting.
At first I just selected the chart and I was unable to select data, so I selected the first data series and was able to select any column I wished, but it added it to the first series.
I just went back to it, and selected the whole chart and attempted to select the column. I could not, so I selected a random column, it worked... sort of... I was able to select the wrong Y column and Numbers selected a column for X, but only some of the rows for X are selected and I can't seem to figure out why. It seems to select one specific column for X, and I can select the Y column. Only 12 of the 15 rows are selected for X, all the rows are selected fro Y. I can go back and manually edit the data series in the inspector. So this seems to be the best option.
Thank you