This product is manufactured by Aldon®
Measure track curvature or visually judge the straightness of straight rail. Steel paddles lock to rail head. The custom 12" ruler measures the space between the rail head and the red-marked midpoint of a 62 ft. cord. Each inch of space between rail and string equal one degree of curvature. Accuracy of measurement is +/-4%.
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.
Weight 5 lbs.