I ran across a formula on this site used to compare lists. It involved ISNA
functionality and I was hoping someone could explain it to me.

As an example, I most often compare two lists to see where there are
discrepancies. Currently I use A1=B1 and move the rows of false responses so
I can see what has been added and what has been removed.

Visually:

New List Compare Old List
Tom TRUE Tom
Dick FALSE Harry
Harry FALSE Sally

becomes

New List Compare Old List
Tom TRUE Tom
Dick FALSE
Harry TRUE Harry
FALSE Sally


This allows me to see that Dick has been added and Sally has been removed.

HOWEVER, the ISNA function seems to be a faster, easier way. I would like
to learn how to use it, but just handing me a formula won't help (as much).

So, what does ISNA stand for? How do you frame the formula (what are the
components of it)? Will it work in a two way comparison (added and deleted)
or does it need to be done twice to achieve full understanding of the changes
between the new and old list?

I thank you for wading through this question and any assistance you can
provide.


--
Please don''t just give it to me, explain how/why so I can stop bugging you
fine people! :)