I have two excel files with the same structure: they both have 1 column with data. One has 800 records and the other has 805 records, but I am not sure which of the 5 in t
vlookup is your friend!
Position your column, one value per row, in column A of each spreadsheet. in column B of the larger sheet, type
=VLOOKUP(A1,'[Book2.xlsb]SheetName'!$A:$A,1,FALSE)
Then copy the formula down as far as your column of data runs.
Where the result of the formula is FALSE, that data is not in the other worksheet.