This is a ancient Chinese calendar used for Gender Prediction.
How it works?
Based upon the age of the "female" and based upon the month conceived.
the application calculates to tell if the expected child would be a "Boy" or "Girl"
Even a simple propability theory will be sucessful in predicting 50% sucess
But this calculator will take the sucess percentage to 75% to 80%
In most of the cases it has worked well.