Stringline Rail Curve Measuring Tool. Measure track curvature, or visually judge the straightness of straight rail. Steel paddles lock to rail head. The custom 12-inch ruler measures the space between the rail head and the red-marked midpoint of a 62-foot cord. Each inch of space between rail and string equal one degree of curvature. Other subsidiary measuring points can be color-dotted on the 62 foot cord. By color-dotting, two different overall distances can be provided in one length of cord, each with its own mid-point. The string reel has a lockable payout/retrieval latch to lock string at any desired point. Accuracy of measurement is +/-4%. Weight: 5 pounds. Product of Aldon® Company