Need a code that creates a popup message box when a certain value is entereted into a cell

Hi all,

I am working with a spreadsheet that contains a column for specific part numbers to be entered, Column "M" in my case.
I need a code that will popup a message box that says, "Treat 1799880 and 2002054 as the same part" when either of those
2 part numbers are entered into a cell in that column. I tried a couple of examples from online but I am not very familiar
with writing code and they just didn't work. The sheet name is DEVIATION LOG if that helps. Any assistance I could get would
be greatly appreciated. I am using Excel 2013. Thanks again.

I could if I knew how to set that up. The only thing I found in Data Validation is setting it for a specific cell, not a range of cells, unless I am missing something.

highlight the range and then click data validation.

xlnitwit,

That worked perfectly! Thank you so much for your help.