Value Plan

Digital value plan with markers
in Paper by 53 app

Personally, I like the feel of the implement in my hand and the "drag" that comes from using real artist's materials on real paper.

However, you will never run out of ink, paper or pencil if you choose the digital app, Paper by 53.
The rewind feature is one I wouldn't mind using on a few of my paintings. :)

For a "real" planning sketch like this, I use Prismacolor or Copic Markers: 30% warm grey, 60% cool grey and black in my Robert Bateman sketchbook.