Help with a combination 'if' and 'sumproduct' formula

[Learning Curve]

Creating scatter diagrams and Excel is looking in the A and B columns for duplicate combos of the (x,y) coordinates. Would someone please untangle this formula for me? =if(sumproduct((A:A=A2)*(B:B=B2))>1,B2,NA())
Thank you!

 

[p45cal]

1. In words, what do you want it to do?
2. What version of Excel do you use?