2½ degree sector of the zodiac, making one twelfth of a sign. There are thus twelve duads per zodiacal sign, each one governed by each sign in order and so repeating throughout the year. This in duration is approximately equivalent to two and a half days, about the time it takes for the transiting Moon to pass through one zodiacal sign. So the Moon passes through all of the 12 signs over the course of a month, just as the Sun passes through all 12 signs in the course of a year. See dwadishamsha.