"S1L1Y1" wrote...
I have Office XP. I am working with Excel How can I check if I didn't enter
something twice?

Depends on the layout of the entry cells. If you're entering into a
single-area range named RNG, you could use a formula like

=SUMPRODUCT((1-ISBLANK(RNG))/(COUNTIF(RNG,RNG)+ISBLANK(RNG)))=COUNTA
(RNG)

The ISBLANK terms avoid #DIV/0! errors when there are blank cells. The
SUMPRODUCT term is the number of distinct, nonblank values in RNG, so
this formula checks that the number of these values equals the number
of nonblank values in RNG. It returns TRUE when all entries are
distinct, FALSE when there are duplicate entries.


Your posting had a follow-up tag set to microsoft.public.excel.misc,
which is a better newsgroup than microsoft.public.office.misc, but you
either multiposted or posted only to the *.office.* newsgroup rather
than to the *.excel.* newsgroup but set the follow-up to the latter
newsgroup. That's generally a bad idea since it fractures threads.
Better to crosspost to multiple newsgroups originally with a follow-up
tag to one of them.