How to detect if a row in a grid has been modified

I have  a grid in a headlerless detail form.  I let users modify data right in the grid itself instead of having a detail screen for editing.

How do I know if users modify a row so when they click on the OK button up on top then I only loop through the grid and update the updated records only?

So if a grid has 10 records and they updated 2 records. Once they click on the OK button, I only need to update 2 records instead of 10.

Thanks

JDE 9.2