Flexometer is an instrument suitable to test lengths. It is a very common tool consisting essentially in a tape, with steel belt, in which a spring automatically rolls up the ribbon inside the reel.
The tape can be unrolled by pulling the free end, releasing the clutch (operable by a button or a lever) to avoid premature wear of the tape and "clutch" itself that locks the tape.
After reaching the desired length, lock the tape with the clutch, preventing the spring to recall it inside the reel, and then read the measurement. At the end of the activity, releasing the clutch, the spring automatically calls the tape, which is always accompanied with sweetness to avoid premature wear.
The tape has a slight curvature along its section, and this characteristic allows, once unrolled, maintaining a certain rigidity. In this way, this tool can be used like a flexible ruler.