In ancient private schools, teachers punished naughty children by slapping their palms. There is a "heart-clearing point" in their palm called Laogong point. Beating the palm with a ruler can not only warn but also clear the heart. Moreover, the ruler is also very delicate. An eight-point ruler indicates tolerance and patience for students' mistakes, and a one-foot-two-inch ruler indicates prevention and warning for angry teachers 120 points.

And confinement, punishment, copying books and so on.

Extended data:

Ruler, a plank used by teachers in private schools to punish students in the old days. Also called a ruler, it is made of two pieces of wood. The two trees incline upward and downward. The upturned person is seven inches and six minutes long, six minutes thick and one inch, and there are wisps of faces on the four sides below. The person leaning on the top is seven inches and four minutes long, five minutes thick and one inch thick, and there are wisps of faces all around.

Put up a wooden buckle in the middle of the upper wood, which is two inches and five minutes long and seven minutes high. Grab the button and knock on the wood below. This ruler is used in rituals such as "conversion, shaving, preaching, speaking" and "eating in the mouth of yoga".

References:

Baidu encyclopedia-ruler