I have another minor problem.

Part of the software I'm working on performs a correlational analysis
between different parameters, and includes the option of including
various "best fit" lines - i.e. Trendlines.

For some datasets I can happily add trendlines, delete them, and change
the type of trendline on the fly. Perfection.

For other datasets this isn't possible. When I look at the chart
manually it is clear that certain types of trendline aren't available
for that dataset. Fair enough.

The problem however is that VBA/Excel allows me to allocate/create a
trendline IN THE FORBIDDEN STYLE using my macro.

Charts(3).SeriesCollection(i) _
.Trendlines.Add Type:=trendtype


It does NOT throw up an error. When I then try to delete/amend the
trendline it acts as if it no longer exists, even though it does!

If Charts(3).SeriesCollection(1).Trendlines.Count = 1 Then
Charts(3).SeriesCollection(i).Trendlines(1).Delete <---- cannot change
properties
End If

For example, with one dataset the logarithmic trendline is not
available, but I can use my macro to create a trendline with type
"xlLogarithmic". This trendline is invisible on screen but does have a
legend key. When I then try to delete the trendline the macro crashes.

Interestingly enough if I change the dataset then the logarithmic
trendline reappears :o) I can then delete it manually.

I have tried trapping the error, but the error occurs AFTER the
trendline is mistakenly added, so I can do nothing about it. It would
help if there was a way to either detect which trendlines were valid
for a particular dataset or if Excel actually created an error during
the allocation of the incorrect trendline :-/

I guess one workaround is to load up a generic dataset which works for
all trendlines, so activating any hidden ones, and then delete them.
Anyone got a more elegant solution?

Bennett