The first file demonstrates normal grid table operation with the same options for all rows in a very simple application, while the second illustrates the use of a custom grid editor select.

You will get some sort of mesh grid on your surface and you will look at a little parallelogram that is an elementary piece of that mesh and figure out what is its area and normal vector.

It will be equally normal for us to be "off the grid" but this fact will also be known and noted.