No it's not real scientific. But it is practical.

Try it with different grits and pressures like I did
the result will be clear. Takes 10 minutes.

The main difference i found is that 220 grit by DA sander removes a lot more material than 400 grit by hand. This is when sanding with normal pressure for normal amounts of time.

: Well....not a real scientific test. Depends on how fast the sander is moving
: and how much pressure you apply, both to the DA and by hand. Can't expect
: one to equal the other if one is slowly sanding with alot of pressure by
: hand and the other has little pressure and is moving very fast by DA.
: Comparing apples to oranges.

: Bill H.