The Chinese Gender Calendar was supposedly discovered by a Chinese Scientist who drew this chart which was buried in a Royal tomb about 700 years ago.

To find the gender prediction, find mother's lunar age at conception (across the top of the table) and then the month in which conception occurred. Follow the column and row to the intersecting point. The color of the box tells you what the prediction is.
Blue = Boy and Pink = Girl

Tool to predict gender according to Gregorian Calendar