@sreilly - Steve: when I need to flatten the back of a chisel or plane iron, I use the magnetic base from a dial indicator to start. Saves me from having to exert pressure using just my fingers. I start with some 80 grit sandpaper on plate glass if the back needs a lot of flattening, moving up to 120, then 150. At that point I'll move to my diamond plates then onto my Japanese water stones.