To measure the amount of cable that is on a reel, it is most accurate to:

Using the footage indicator stamped on the cable is the most accurate method for measuring the amount of cable on a reel. This indicator is specifically designed to provide an exact measurement of the cable's length based directly on the manufacturing process. Therefore, it reflects the actual footage of cable rather than an approximation or dependence on external tools.

This method eliminates the potential for human error that could occur with estimates or manual measurements, such as using a folding ruler, which might not fully account for the full shape and capacity of the reel. It also avoids the inaccuracies that could arise from counting wraps on the reel, which may vary based on how tightly or loosely the cable is wound. Consequently, relying on the stamped footage indicator ensures that users have a precise and reliable measurement of the cable available.