Hi Guys

Is it possible to sum trendlines, or simply series, in excel charts?

I have a large spreadsheet recording financial expenditure in respect
of about 10 different job numbers, with each of these graphed on the
chart showing trend lines. The problem is, if you simply chart the data
in aggregate in order to find an overall trend line for expenditure,
ie. set the source data to the various columns under each job number,
there are large numbers of transactions under different job numbers on
the same date, which means that these transactions aren't summed but
appear as different points on the chart, resulting in an incorrect
trendline. So is there some sort of function to add together trendlines
or series in charts, or alternatively, is there another way of
achieving the same outcome: an overall trend line for multiples series?
Thanks for your help,

Cheers

Simon