Winding Sticks

I made this pair of winding sticks in the woodworking class I took recently. They are a traditional tool used to make it easier to detect twist, or wind, in a narrow wood board. It was an excellent training exercise for improving hand plane skills, requiring planing six edges flat, square, and parallel. 

Here's the Wikipedia description of how to use winding sticks -- or you could just look at the extra photo:

One winding stick is placed on one end of the piece and the second winding stick is placed on the other end, but parallel to the first. The woodworker then stands back a short distance and sights across the top of the two sticks. If the surface on which the sticks are sitting is flat (in the same plane), the top edges of the two sticks line up perfectly with each other; otherwise, the discrepancy becomes apparent. Adjustments to the surface of the board are then made (e.g., with a hand plane). This process is repeated all across the piece until the piece is satisfactorily true.