:: THE IMPORTANCE OF THUMBNAILS ::
We're not talking your finger here. Any time I work on a book with another creator I provide him/her with thumbs of any pencils I'm doing. I work in half scale or quarter scale of a full-bleed artboard.
I have a small thumb size that, when enlarged by 400% equals the full artboard size. This allows me to print out my pages and rework them on my light table. This way it is much easier to keep the exact composition I created in my thumb.
I also have thumbnail templates for 50% standard comic book size. This gives me a little more room. These smaller sizes are great for roughing out perspective as well. You don't need to use a yard stick with such small pages.
There is a great description of thumbnail usage in the book Panel Discussions which is the book list which was the first post in this blog.