One of the interesting, novel things about working digitally is being able to work on layers and separate and inspect different aspects of a drawing or painting. If you're not familiar with layers, many graphic programs use them and they can be best compared to drawing on several sheets of acetate or clear paper. This lets you draw aspects of the image separately so you can decide if something's working without having to erase a lot of work. There are many other uses for layers as well. At top I've isolated just the outlines and blacks and at bottom it;s just the hatching. I find being able to see a drawing this way can really help steer it in the right direction.