Hi Rf,

Say your x data is in A1:A10 and your y data in B1:B10

Put this in C1
=TREND(B1:B10,A1:A10,A1)+STDEV(B1:B10)
(note the A1 is for the *first* point in your series)

and this in C2
=TREND(B1:B10,A1:A10,A10)+STDEV(B1:B10)
(note the A10 is for the *last* point in your series)

Now go to source data and add a series with
X-Values =(Sheet1!$A$1,Sheet1!$A$10)
Y-Values =Sheet1!$C$1:$C$2

You can then set the series to show a line but no marker
or add a trendline if you wish.

HTH
Martin


wrote in message
...
I have a historical stock price chart into which I've inserted a
trendline; I'd like to now show a line graph with one standard
deviation above the trendline and one below; ideas please?