>>- In the rigthmost column of the grid I put a command button with a downarrow icon (this makes the thing intuitive)
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>This does sound cool, but isn't a simple Add button underneath the grid even more "intuitive"?
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>That's what I use. Zero learning required. :) And I don't begrudge the screen real estate, since I also have a Delete button.

I don´t want the user to go out & back in the grid. the less the user uses mouse, the faster they write data. And with a delete button outside the grid, the user needs to pay attention and make sure wich record´s active so they don´t accidentally delete the wrong record while a Delete button in each record is more clear.