I have a worksheet ("All SEG ISBNs") which is a long list of numbers in
Column E. I have another sheet "WH ISBNs") in the same workbook with a long
list of numbers in Column A. Is it possible to write a macro that will take
each one of the numbers on the "WH ISBNs" sheet, look for it on the "All SEG
ISBNs" sheet, and, if it finds a match on the "All SEG ISBNs" sheet, add the
text "WH Match Found" next in Column F on the "All SEG ISBNs" sheet--that is,
next to each of the matching numbers? There may be duplicate numbers in each
column on each sheet, and it's OK if the macro inserts "WH Match Found" next
to each occurrence. (By the way, both sheets have header rows.)

I've used the COUNTIF function to identifying matching numbers, but it seems
to take a very long time to calculate. If was hoping that a macro-based
version would be faster, and besdies, I'm hoping to do this same thing for
other sheets in the same workbook, and the calculation time for a
formula-based solution is just going to get worse and worse.

I've poked about and found various macros that seem to come close to what I
need, but frankly, I'm not knowledgeable enough to manipulate them well, and
my various attempt to loop and whatnot keep ending in disaster.

Any help would be much, much appreciated!