A flexible curve lets you copy just about any curve, but this flexible curve also gives you a precise measurement of the curve. This might come in handy in knowing exactly how long the stock needs to be before you bend it, for example.
This plastic curve is stiff enough to hold its shape while flexible enough for you to match it to curves and other contours. On one side of the curve a scale measures inches in 1/16″ increments and on the other it measures metric in 1mm increments. The raised edge makes it easy for you to transfer the curve with a pencil.
MLCS sells the flexible curve ruler in 12″, 24″, or 36″ lengths for $10, $15, and $19 respectively.