I input data for a survey company and come across roughly 300 new numbers a day and i have to make sure none of these numbers are duplicated within the day and including any previous numbers i have ever inputted into the spread sheet. Right now my only solution to this task is scrolling through a list of about 10,000 every morning after putting them in descending I watch the last digit in each number and if i ever come across two last digits that are the same then i check the preceding numbers to see if they match. Is there any formula or tool that might help me complete this task more efficiently?