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Well how i learned was by trying it. For instance i learned to wet sand like a week ago. I watched a bunch of videos on how to do it. I started with a really fine sandpaper so I would not take off to much and just trial and error. I started with very little pressure and learned I needed to press just a tad harder. I would whip of the area to see if I could see the scratch. If I could I went a bit more. I did that until the scratch was very hard to find. I was working on a gx460 with 116000 miles on it. I took out 10 scratches with no problems. Its much easier than you think.