Pinduoduo calligraphy ruler can sink, which refers to a kind of calligraphy supplies sold by Pinduoduo. Its main feature is that it can sink into the water without floating. This ruler is usually made of impermeable materials, such as plastic or rubber, which can be put into water to fix the paper during calligraphy practice to prevent the paper from moving or shaking, which is helpful to improve the stability of calligraphy practice. The design inspiration of this ruler may come from the inkstone used in traditional calligraphy practice, which is also relatively heavy and can fix paper and ink. However, the specific product details and performance need to be further reviewed in the description of the sales page and user evaluation.