Excel Tip : Prevent Duplicate Data Entry Using Data Validation and COUNTIF Function

****SUBSCRIBE****** To my Excel at Excel Newsletter 3 FREE Excel Tips First Wednesday of EVERY Month http://www.howtoexcelatexcel.com and get my free Top Tips for Excel Ebook Immediately ****Other Places You Can Find Me For More Excel Tips*** ++Website http://www.howtoexcelatexcel.excel.com ++Twitter https://twitter.com/howtoexcelatex ++Pinterest http://www.pinterest.com/howtoexcelat Learn how to use your own Auto Correct options in Excel to reduce or eliminate data entry errors.