Rob

Certainly you will have to return #N/A to stop the chart line dropping to
zero. Outside of code you would use ISERROR or ISNA to trap this #N/A
returning a value of say, 0...not sure about how your SLOPE construct is
built, but hope that gets you in the correct direction and re-assures you
that you have the right route with the chart with #N/A

--
HTH
Nick Hodge
Microsoft MVP - Excel
Southampton, England
www.nickhodge.co.uk
HIS


"Rob Kings" wrote in message
...
I'm having problems with a User Defined function.

I have a chart (line graph) based upon a column of data calculated by a
UDF. I also have another cell that is the slope of a range of the column
using the SLOPE function.

Now, if for any reason I can't calculate a value in my column (e.g. some
of the parameters are missing) I'm not sure what to do:

1. If I return #N/A (Using CVErr(xlErrNA)) then my graph is OK, but the
SLOPE function also returns #N/A (Though the chart has a trend-line which
does have a slope calculated and displayed)

2. If I return "" then the line drops to zero

3. If I return Null then this is being taken as 0 and once again the line
drops to zero.

4. If I delete the formula from the cell then it appears as blank, and
there is a dis-joint in the line

So, how do I get the chart to appear OK (with no disjoint) without mucking
up SLOPE() and what is the difference between a cell with no value and a
UDF that returns Null (or a zero-length string)

Help. I'm very confused.

Rob