Use an "XY (Scatter)" chart.

When you selected a "Line" chart, you (by definition) told Excel that your
x-axis was categorical instead of numeric, and that what you provided for the
x-axis was a set of category labels that may or may not have numeric values.
Why Excel would offer to fit a trendline in that circumstance is a mystery to
me, but when it does, it uses x-values of 1,2,3,... and correctly calculates
the regression of y against those assumed x-values.

Jerry

"Jan M." wrote:

Hi,

I created a bar chart in Excel from the following data:

X Y
73 6.6
78 5.7
86 4.8

The SLOPE and the INTERCEPT functions returned -0.136 and 16.4448
respectively. The resulting equation is Y = -0.136X + 16.448 which seems good
enough to me.

Then I added a linear trendline to the chart. Excel displayed the following
equation: Y = -0.9X + 7.5, R ^2 =1 which is way off (and it's not a rounding
problem)!!!

The data seemed farly linear to me, how come Excel can't come up with the
right equation???

Thanks

Jan M.