Help for a "Surface and Flux integrals" program

[Arno K]

That is weird, must first check it, as there are always 4 arguments the usage of no list may be better.Without that list entry it seems difficult to force an error that then writes the help text, so we need an iferr around the whole computation.
Why now the error condition always is triggered, hm. Replace in IF: TYPE(w)≠4 by type(w)≠ DOM_LIST then this is gone and your example provides about approx 804.57.