Determination of the baby's sex
It's unscientific, but it surprisingly works.
There is such an unscientific method of determining child's sex - we take the woman's age at the moment of conception plus the two last digits of the year of conception and the sequence number of the month at the time of conception. If the resulting number is odd - it's a boy, if it's even - it's a girl. I applied this to my children and the children of my friends - it worked. Strange but it's true.