Hi,

The use of additional series is the way to do it.
There are more alternatives explained here.
http://www.andypope.info/charts/averageline.htm

Cheers
Andy

--

Andy Pope, Microsoft MVP - Excel
http://www.andypope.info
"Gaijintendo" wrote in message
...
I was adding an average line like this

Series 1 Series 2
10 average(series1)=25
20 25
30 25
40 25

and plotting the average line.

I then tried plotting a linear trendline, with the 'set intercept' set to
the average (25). However the lines were not always perfectly horizontal
(I
can't understand why).

Is there a way to create an average line?