Magnification of brush size

I have spent years going back and forth in the slider to get the right size of brush, especially as it pertains to dodging and burning, erasing, etc. The increments jump in huge chunks when done manually (the keyboard arrow button is too tiny an amount for each click) and some, where they land (e.g., 1101... 01?), suggest there is some sort of predetermined amount. An accumulation of literally hours has been spent selecting the precise size in the upper left slider before applying the action. All these sophisticated things keep coming on line -- which are great -- but I have to complain a little.