So in a store where I work, we don't have that many products about 1700 and we were doing stock check last week, and I devised a much easier method for it.

I exported stock data from our pos software to excel and was left with id. An id of the product, name and how much we should have. So I just added a countif function and we started scanning the products barcodes for ids. The id were just being listed in a seperate sheet while the stock counted itself.
Works like a charm. The only problem was - what if the computer cays we dont have something thus not listing it and we scann it. So that was easy to find - that number would only repeat 1 time in the whole sheet so with count if and if functions it now says error besides the scanned id.

Now i was wondering if there is an easy way to collecting all the errored id's in a seperate sheet. I tried using lookup and vlookup but its not working.

Any tips and ideas appreciated.