What is the Chinese gender predictor?

The traditional Chinese method for predicting the gender of a baby is to know the birth date of the mother and the exact date of the conception of the fetus. This is based on an ancient method by an unknown monk who devised it using a lunar calendar.

This method is contained in a chart found in a royal tomb in Beijing and claims to have a 90 percent accuracy compared to Western methods. This chart supposedly works well when the mother's age is computed correctly (which is to add one year at the age of conception) and the date of conception as based on the Chinese lunar month.