The hitching line makes a circle around the disk to obtain a line segment equal to the circumference length. The measured circumference length is divided by the known diameter of the disk to obtain the circumference ratio, π.

A measurement tool for circumference includes at least one disk with a circumference thereof provided with a through hole; a straightedge provided with a fixed post and a plurality of scales, and the fixed post penetrates through the through hole to fix the disk to the fixed post; and a hitching line with one end thereof penetrated by the fixed post, and the other end of the hitching line surrounds the disk or straightens along the straightedge.  If a diameter of the disk is known, the length of the circumference is divided by the diameter of the disk to obtain a ratio of the circumference.

(1)此量測器具適用於全球中小學數學教育，製作簡單國內企業界皆可實施。

(2)製造成本低容易獲得國內公司授權。

(3)因為是全球性，國內外交互授權之可能性高。