Boy or girl?
The Chinese conception calendar was published in the 13th century by a Chinese scientist. Using this formula, you can supposedly predict based on the mothers age (at time of conception) and the month of conception, the sex of the child.
The Chinese scientists discovered and drew this formula, which was settled over 700 years ago a royal grave near Beijing. The original is in the Science Institute in Beijing. The correctness of this calendar was established by thousands of people and is reported at 99%.