Whether I’m cropping a one-of-a-kind reference photo (like the one at right) or simply need an easy way to tack up a sketch, one item I find extremely useful is a metal board with long, adjustable magnetic rulers. Found in any craft store, the board is designed to aid knitters and needlepointers (they put their pattern on the board, and use the magnets to “underline” the row they’re on). As an added bonus, I use the rulers to measure the image before I transfer it to paper.
Another item I find useful is a door “peephole,” which can be purchased in any hardware store, usually for less than $5. We all know how important it is to stand back from a piece of art and get a view from far away. Using this viewer, the piece appears to be far away, but since it’s still right in front of me, I can easily make corrections and look again without having to scurry back and forth from my easel or table.