A conception chart is a bit more useful for having a child than for avoiding having one, though they can be used for both. The western conception chart only claims to be able to predict cycles of ovulation and tell you when you will be the most fertile so that you can be sure to have sex on those days, while the chinese conception chart claims much greater powers. The chinese conception chart claims to actually be able to predict the child's gender based on the phase of the moon, the mothers age, and a variety of other factors, but most people are skeptical to say the least.