I've been taking a certification course on Excel. It's a beginner class but something caught my attention. Specifically, Data validation.
We learned how to do it using the default conditions but I would like to include my own using formulas.
Here is where I'm at:

Now, what kind of formula would I put here? Would I use an if? If so, what would I return? Would I return TRUE or FALSE?
I think the best way for me to learn would to be if somebody showed me an explicit example of one. So, for that purpose, here is a situation:
If B2 is exactly 28000, throw the validation error without using the default validation criteria. Thanks guys :)