Me*

Help a brother out!
I have a register of all the inspection and test equipment that my Quality Control crew in the field have in their procession. The register shows (along with a bunch of other random crap) the date it was last calibrated, and the date it is next due to be calibrated.
I'm not too bad with excel basics, but am far from a programmer. I've mostly got the sheet working like I want it too. I'm just having a few issues with some minor tweaks I'm trying to do.
Basically, in short, I'm using:
K7-TODAY() to tell me the number of days until the item is due for calibration
Where cell K7 is the date the calibration is due.
I'm using conditional formatting to highlight the cell if the value is less than 20, which is handy, but I wanted more of an action/circumstance than that. For example, a pop-up or warning box.
So I'm also using data validation too, which makes a pop-up if the data in the cell is outside of a specified range. Problem is, that these both work perfectly when you manually enter data into the cell, but if the cell is updated using a formula ie K7-TODAY() the data validation pop-up does not occur (only the conditional formatting)

Has anyone tried to do something similar? Is there a way to make the data validation too work when the cell is updated using a formula?
Or maybe there's a better way to achieve what I'm trying to do.

Come at me!

Cheers

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