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When we write with a common ruler, the ink will stain the paper if we move the ruler carelessly over our writing. Traceless Ruler is designed to solve this problem with special a structure.
Traceless Ruler has an arched structure and a slot in the middle with scale. Due to the arch, a gap is left between the ruler and paper while writing, so the ink won’t leave any unexpected trace on the paper even you move the ruler carelessly.
Jinghua Zeng Yuqin Shi Xiaoliang Wu Binghao Jiang