Compact Multi-purpose Marking Tool 15mm (for drawing horizontal, vertical lines, and grids)

I found that most of the hundreds of hard-pen calligraphy practice papers I've finished have unused backsides. Driven by environmental principles (and a need to save money), I hereby made a simple marking tool.

The grid spacing is 15mm, allowing for 10x14 Chinese characters to be written. It can also be used to draw horizontal and vertical lines independently. When not in use, the two plates can be combined into one for storage.