CONSTRUCTION: It is composed of an inner rubber protection layer, middle rubber layer, steel wire spiral layer and external rubber cover.
结构：由内胶层、内胶保护层、中胶层、钢丝缠绕层和外胶层组成。
External plastic or rubber material, laundry ball of about 5 centimeters in diameter.
外部是塑料或是橡胶材质，洗衣球直径约5厘米左右。
But because the extension of the rubber band is not directly proportional to the external force, the scale of the rubber band can not be divided equally.
但由于橡皮筋的伸长与所受外力不成正比，故不能等分地进行刻度。
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