Why does a standard watch have two rows of scales?

Two rows of scales, one for measuring the length of the shadow and the other for measuring the direction of the shadow.

According to Baidu Encyclopedia, there are two rows of scales in the standard table because one row is used to measure the length of the shadow and the other row is used to measure the direction of the shadow. Ghost table is an astronomical instrument for measuring the length of the sun shadow, which consists of ghost table and ghost table. A straight rod perpendicular to the ground is called a watch, and a scale is engraved on the ground horizontally to measure the shadow length. Every noon, the shadow of the table is projected on Guimian. From summer to the sun, the sun shines directly and the surface shadow is the shortest; On the solstice of winter, the sun is oblique and the shadow is the longest. Therefore, the winter solstice and summer solstice can be determined by measuring the length of the shadow, and the solar terms of a year can be calculated.