If you're sanding for wave removal, remember this, you can't remove wave with fine grit papers,
you'll only polish it. To really get rid of wave you need 600 or more coarse to remove it.
Some say they can get rid of it with a hard block and a finer paper than that, say like 1000, but
I find it easier to just start with 600 to 400 and be sure, with the coarser papers you don't even need a
very hard block, I use a soft one for those grits and it gets it straight, but you have to make long
strokes to get it straight.
I've done one panel starting with 400 and then the adjacent panel starting with 600 just to compare,
I could tell a difference between them when I finished buffing, very slight but the 400 was straighter.
This procedure is way to good for my everyday collision repair work, for that, like I said earlier,
I just use a 1500 or 1200 disk followed with a 2000 one, plenty straight for that, like the motorcycle
gas tank in my avatar.