Nev -

A scatter chart uses real data values for the X coordinate. The error
that results from using categories (which Excel treats as 1, 2, 3, etc.)
depends on how different the real data is from a simple set of counting
numbers.

One major cause of inaccuracy is simply in not showing sufficient digits
in the trendline formula. When the formula is showing, you should double
click on it, select the Number tab, and choose a Scientific format with
lots of digits showing.

- Jon
-------
Jon Peltier, Microsoft Excel MVP
Peltier Technical Services
Tutorials and Custom Solutions
http://PeltierTech.com/
_______

Nev. wrote:
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.