What criteria define a woman as having a customary menstrual cycle ('mu'tadah')?

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A woman is considered to have a customary cycle only when she knows the duration of her cycle, her time of menstruation, and her time of purity. The lunar cycle ('shahr') is the duration containing both menstruation and purity. The minimum cycle is fourteen days, consisting of one day of menses and thirteen days of purity. If the minimum purity is established as fifteen days, the shortest possible cycle is sixteen days. There is no upper limit to the cycle's length due to the lack of a limit on the duration of purity. If a woman knows her usual cycle, such as thirty days with five days of menses and twenty-five days of purity, and knows its commencement, she is considered customary. Knowing the days of menses and purity, or just knowing the cycle duration, establishes her status. If she knows the days of menses but not purity, or vice versa, she is not considered customary.