The tape can be rolled up because there is a spring in the tape. When the measuring length is pulled out, the length of the ruler and the spring is actually lengthened. Once the measurement is completed, the spring in the tape will automatically shrink, the scale also contracts under the action of spring force, so the tape measure will roll up.

First, the tape is too deformed and will not fail. Why is it not invalid? The wind-up in the tape measure is very long, and its range from completely relaxed to complete tightening is very large. The whole stroke of the tape measure includes the margin at both ends, so the tape measure will not fail.

Second, pull one meter long and pull two meters long, there is no difference in pulling force; The wind-up of the tape measure is very thin, and the deformation when tightening is also very small, so the reaction force is very small, and the change of force is not felt when measuring tape.