The tape measure head is loose so that we can measure the size. There are two measuring methods when measuring the size of the tape measure. One is to hang on the object, the other is to top the object. The difference between the two measuring methods is the thickness of the iron sheet on the head of the tape measure. The purpose of the loose head of the tape measure is to compensate for the iron piece on the head of the tape measure when it is placed on an object.

The "inner core" of the tape measure has a small piece of steel inside, which acts like a spring. You can also think of it this way, that is, the small steel wire on the toy pistol trigger that is used to "strike" the bullet. Small, less than the elasticity of the small steel wire) disappears, so it automatically rebounds. And there is a folded part on the front of the tape measure, which works at this time, so that the tape measure is stuck outside so that it will not be completely retracted. He was loose at the beginning, but after pulling it out, he became tight. After letting go, it should have a recovery process, so it will automatically bounce back again. It's just that the inside is loose at the beginning, and it becomes tight when pulled, and there is an elasticity between it, and when it is loosened, it will naturally bounce back.