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Also known as the Chinese Pregnancy Calendar and the Chinese Gender Predictor, the Chinese Gender Chart is reported to be many thousands of years old and is on display in the Beijing Institute of Science.

The chart is supposed to predict whether a pregnant mother will give birth to a boy or a girl. The chart gives its prediction by simply reading the relevant row and column referring to the mother's age at conception and the month of conception.

You will find more information here, or you can view the the Chinese pregnancy calendar here.