The key to these outstanding pencils is the perfectly fat eraser that is over an inch long. Its formulation is excellent (neither too hard nor too soft) so it erases superbly and lasts quite a time, and it has refills in packs of three that can sometimes be found in Office DepotMax.
I must also suggest a lead softness/hardness of 2B, instead of the normal "Number 2 pencil lead" that is standard for test taking here in America. It glides onto the paper more smoothly and yet erases easily and mostly completely.