Been playing with UDF's in .xll add-ins and found that these are indeed much
faster than VBA UDF's.
In a moderately complex math function I found it about 30 times faster.

Just one thing I don't quite understand:
I have the xll function in B1 and the VBA function in C1
Now I copy both down to row 65536.
All cells in column B are calculatated in about 1 second,
except cell B1, which is done last. This is done after the last cell in
column C is done.
Swapping the columns (XLL in C and VBA in B) makes no difference.

Any suggestions why this and if anything can be done about it?

RBS