I have 3 sets of data for different conditions. When charted, 2 sets have the
option to "add trendline", but the third set (with more "ups and downs' in
the data) does not have the option available. There are no empty cells in the
source data nor are there multiple series on the chart. Any ideas why I don't
have the ability to add a trendline on this set of data. At first, I thought
it was perhaps because there isn't a high enough order in the polynomial fit,
but paring down the data so there is only one peak did not help (that is, add
trendline was still not an available action).