Hi,

1. Select the series and choose Chart, Add Trendline, select the Options tab
and enter a value in the Forward box.
2. On the same tab you can use Ed's suggestion to display the equation Excel
is using for the trendline. You can buld that equation in the spreadsheet
and use some of the extrapolated x-values to calculate the y-values.

Cheers,
Shane Devenshire

You can also,

"paul in leeds" wrote:

hey, i want to extrapolate a number from a graph but cannot see how to do it.
i have a line graph with concentration along the bottom, and effect of change
in concentration on the y axis. Is there any way i can link in some extra
values in to discover the concentration of some unknown results?
Thankyou Paul