Tim Zych wrote:
You lost me when you said:

"planes orthogonal to the xy-plane"

OK--planes perpendicular to the xy-plane

Wow. For me

Worksheets.Add
or
ActiveWorkbook.Worksheets.Add

add new sheet(s) to the active workbook, and never to the Addin.xla,
assuming the addin has the IsAddin property set to True or is hidden.
ThisWorkbook.Worksheets.Add adds the sheets only to the Addin.xla. Just to
confirm, you have different results?

No, I don't (although I said 3 times that I do!). Turns out that prior
to running the calling Sub I had manually activated the worksheet in the
Add-In and never reactivated a worksheet in my testing workbook before
running the code. So---Never miiind :-)

Thanks for spending time on my pointless posting; sorry.

Regards,
Alan