Excel "Insert Formula" dialog always call my user defined function
 

I know there is a way to do that by enumerating all to-level windows
and checking for "bosa_sdm_xln" where 'n' is the version of Excel.

The problem is that I have to do this check at each call of my user
defined fonction which is called very often and I lost a lot of cycles
there (I used a profiler to check that)

Is there any other way to do the same?

Thanks

Nic