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.