Match and show non matched

Hello,

I use the match formula all the time! But today I ran into an issue. How do I find out what did not match???

Example:

Sheet 1 Column A Column B Sheet 2 Column A Column B
WF69508 WF69508 1
WST2560 1


See if I use the match formula that I have than sheet 2 gets matched perfectly with sheet 1 for the WF reference #.

But I want a formula that tells me or will list on Sheet 1 the reference numbers that did not match like WST2560 since that reference # is not on sheet 1.

Thank you for your help!