“Winding sticks” are invaluable when you are dimensioning boards with hand tools, helping you to keep track of both flatness and twist (or “wind”). To check for twist, you place a stick near each end of the board or slab and then sight across the two. Some folks make their own straight sticks from scrap wood, but this takes time and expertise. Also, wood sticks can warp over time. Instead, you can use two aluminum L-bars from your local home-improvement store.