The Laws of Family Purity (Taharat Hamishpacha) are quite complex. One of the components of these laws is to anticipate the upcoming period and intimately separate at that time. The purpose is to avoid intimacy at a time when a woman may become ritually impure due the onset of her period. Most women will anticipate the onset of their period according to three methods: 1. * The exact Hebrew date their previous period began (Veset HaChodesh) 2. * The Average 30 day Cycle (Onah Beinonit) 3. * Cycle based on interval of time from one period to the next (Haflaga)