Dave -

Do you have any physical basis to use one over another? In other words, if
it's a physical phenomenon you're plotting, is there some theoretical
relationship that describes the phenomenon? If so, use the trendline of that
form, or transform the data until the model matches one of the available
types.

If you want a nice-looking, smooth fit, you could use a polynomial, but
people usually take this to extremes. There is no physical basis for a sixth
order fit. You should use the simplest equation that shows a reasonable
agreement with your data.

If you are using the fit for interpolation, use your judgment. Try to avoid
using a fit for extrapolation, especially a poly fit.

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


"Dave" wrote in message
...
I am new to trendlines.

I am using an xy scatter graph. Is there rule for when to use the
different
types of trendlines?

I presently use a Power Type, but I am not sure if this is giving me a
true
tend.

Thanks