First, when the font is regular script, the horizontal line is basically upward.
The basic form of regular script horizontal is left low and right high, its angle is generally 5 ~ 8 degrees, and the oblique horizontal is 8 ~ 13 degrees.
Due to human vision, in regular script handwriting, horizontal lines are basically not flat, but appear in the form of low left and high right, and only the angle of horizontal lines changes.
Second, when the font is running script or cursive script, the horizontal line will appear downward.
The writing of running script and cursive script is to dissolve the writing method, and more obviously integrate the emotional expression of calligraphers, especially cursive script, which can be said to subvert the creation of Chinese characters and further simplify the situation of symbol replacement. Therefore, there are various ways to deal with horizontal strokes in writing.
In addition, the writing of calligraphy works still follows the ancient top-down and right-left ways, thus further weakening the main expression of horizontal lines in writing.
To sum up, the horizontal strokes of calligraphy are regular script font up and cursive script font down.