Step 1: Use a standard protractor to measure the four external angles of the outer disk respectively, and check whether it is 90 degrees. If the error exceeds 0. 1 degree, it should be polished.
Step 2: Check whether the ten lines of Tianxin are parallel to the four outer edges respectively. If they are not parallel, adjust the position of threading holes properly. Check whether the four threading lines are located at the midpoint of the four outer edges respectively. If they deviate from the midpoint, reopen the hole.
Step 3, check whether the intersection point of the celestial center reticle is aligned with the vertex of the magnetic needle thimble.
Step 4: Align the four endpoints of the celestial center decagonal line with the inner disk at 0 degrees, and check whether the other three endpoints accurately point at 90 degrees, 180 degrees and 270 degrees. If there is any error, find out the reason in detail and adjust the position of threading hole appropriately until it is qualified.
The best way is to use an electronic geomantic compass to check the accuracy of the degree, or simply buy an electronic geomantic compass metaphysics, and you don't need to calibrate it once in your life.