No, there is no rule that a trendline is automatically inaccurate for
anything other than a XY Scatter chart. It all depends on what you
have on the x-axis.

Suppose you are plotting week number (1, 2, 3, etc.) on the x-axis and
some kind of a score on the y-axis *and* you have data for each week
between the start and the end of the season. Then, a line chart will
be just as accurate as a XY Scatter chart.

Or, if you use dates on the x-axis and leave a hole for the score for a
week when the team doesn't play, by default XL will use a 'time scale'
for the x-axis in a Line chart. In this case too the trendline will be
accurate.

--
Regards,

Tushar Mehta
www.tushar-mehta.com
Excel, PowerPoint, and VBA add-ins, tutorials
Custom MS Office productivity solutions

In article ,
says...
I have been trying to analyse some non financial data with Excel.
I did pay to do an Excel course of several weeks, but they only
touched upon accounting uses but nothing on statistics.
I am very much a novice with Excel.

I have beening doing line graphs combined with trendlines.
I recently read that trendlines are not accurate unless
scatterplots are used.

So can someone give me a rough guesstimate what the
range of that inaccuracy might be? And a very brief idea
of what might cause that inaccuracy?

TIA,

Nev.