Oh, good grief. This isn't a mathematics forum. It's an Excel forum.
You know.. Excel? The spreadsheet program? Sorry, I have no idea what
you're talking about... "round k down to the nearest 1e-4 Newton
Raphson blahblahblahwhoopeekipperedherring."

I thought iteration simply allowed a formula or calculation to repeat
itself until a certain value was reached. In this case, increase P4 in
increments of .0001 until N501 = 8,800,000.

Normally, when somebody posts a question on this newsgroup, the person
replying will suggest a VBA script or tell them what to type in the
formula bar, not throw a bunch of propellerhead math mumbo-jumbo at
them. Ya'know? Sigh.

Ron M.