I have a function that reads the coefficients of a trendline by
searching the datalabel.text It is by no means sophisticated, but it
works well. It is designed only for second order polynomials and
returns the a, b, or c coefficient (y=ax^2+bx+c) based on the user
"reference". That is =coeff("a") returns the a coefficient.

My question is....since the function doesn't truly reference anything
but the code, it doesn't update when the underlying data changes.
When the data changes the trendline is updated, but nothing triggers
the function to "recalculate". Is there a way to reference the chart,
such that when it changes the value is recalculated?.....will this
even work like changing the value in a referenced cell??

Thanks,
John

Public Function coeff(var As String) As Double

sEqn = Charts(1).SeriesCollection(1).Trendlines(1).DataLa bel.Text

fst = InStr(1, sEqn, "x2")
snd = InStr(fst + 1, sEqn, "x")

If Mid(sEqn, fst + 3, 1) = "+" Then
bsign = True
Else
bsign = False
End If

If Mid(sEqn, snd + 2, 1) = "+" Then
csign = True
Else
csign = False
End If

If var = "a" Then
coeff = Mid(sEqn, 5, fst - 5)
ElseIf var = "b" Then

If bsign = True Then
coeff = Mid(sEqn, fst + 5, snd - (fst + 5))
Else
coeff = "-" & Mid(sEqn, fst + 5, snd - (fst + 5))
End If

ElseIf var = "c" Then

If csign = True Then
coeff = Mid(sEqn, snd + 4, Len(sEqn) - snd + 3)
Else
coeff = "-" & Mid(sEqn, snd + 4, Len(sEqn) - snd + 3)
End If

End If

End Function