Tell fortune to the blind.

How do blind people calculate a perpetual calendar? What is the formula?

Good question! That blind man does have a fortune-telling method. Whether you give him the date of the solar calendar or the lunar calendar, whether it is decades ago or hundreds of years ago, he will soon be able to accurately calculate the eight characters! They use the name "meteor chasing the moon". Unfortunately, that set of "shooting at the stars and catching the moon" is only for the blind, but not for the discerning. If the discerning person uses it, he will be blind over time.