roughly 300 grit sandpaper. They sold them in expensive pads you could put three fingers in. After two go arounds- I just found the right sandpaper and made my own.
Move it in gentle circles and in about 15 to 20 mins it starts to get very fine and disappear.
Occasionally I get a burn but I never ever get an ingrown hair. If I oversand it gets bristly from the little stubs sticking out of the skin but if I do it right, it is almost invisible and there is minimal stubble.