According to the national standard GB/T2-20 18, the standard size of ballast is about 45cm×4.5cm, and the allowable error is 0.5cm ... This standard size is determined after comprehensive consideration of various factors, which can not only meet the needs of calligraphy practice, but also meet people's habits and comfort. Rulers commonly used in calligraphy are 30 cm to 40 cm in length and 3 cm to 5 cm in width.