You could do this with formulas:
Add another column to Sheet1 (today's list) and reference Sheet2 with the
formula
Say that column A contains the identifier common to the orders.
Column M is where you decide to put the formula

In cell M1 use the formula
=Countif(Sheets2!M:M,A1)

fill this down and watch the fun...

You could also build a loop in a macro and have it do this for you.
The macro can be more generic and could work on any sheet you choose.
But the principal is the same.

hth

--
steveB

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"AB" wrote in message
...
We're building a spreadsheet that lists all the orders we need to ship out
in
column A (by order number). Other columns provide data. There are about
500
orders per day.

Each day we add a new sheet and delete the oldest one, so we constantly
have
the orders needing to be shipped out for the past 30 days.

I've been trying to find a way to take the orders on the newest sheet and
see if they match orders on previous sheets, then change the color of the
entry number on the newest sheet to alert me that it's an order holding
over
from the previous day.

Theoretically, I'd only need to compare each record against those the
previous day.

I can't seem to find a conditional format that works properly and I don't
know all of the VBA-coding functions well enough to do this on my own.

Can someone help?