As you see here, I am working on another line drawing for my book. Instead of drawing the borders to size in pencil, I simply let a double-thick mat be my border. Easy peasy. No measuring.
A few months ago, I was perusing a lovely book about Tasha Tudor and I noticed her doing this in a photo of her sitting at the kitchen table, sketching. Since she is one of my goddesses, I thanked her, kissed the book, and immediately went to try it. Works wonderfully. I imagine anyone working in pastel already uses this method, as it keeps the edges of your paper dust and fingerprint free. (You would think I'd have come up with this earlier, after having drawn dozens of black and whites. )
I should be finished with this drawing today. This was a two and a half movie sketch. It should be only a one movie line drawing. Were I to paint in the black areas, that would take another movie or two. Once I finish the line drawing, it takes me another one or two hours to scan it, clean it up and format it on the computer. ( "Clean it up" means erasing any stray lines or mistakes, adjusting the contrast, eliminating any pencil marks that didn't erase, etc. - all on the computer after it is scanned.)
So, by the end of today I should be done with another page for my coloring book.