So anyway they now make these very thin, little metal plates with a number of shapes cut in them, that you can use as templates to train your eraser on particular small areas of a drawing. When you're doing very large, finished drawings, it's a drag erasing because you need to rub fairly vigorously, or in a back and forth motion, that inevitably removes far more of the drawing than you'd like. Using one of these small (and cheap) eraser templates, you need no longer worry about collateral dammage, so to speak. You can now precision target the desired area, and with a firm eraser, easily remove it. Indeed, I've also used the template to add shapes to the drawing, so that one can subtract or erase creatively!

I should add the one I'm using is made by Danish company LINEX...