In astrology, a dwadasamsa, which is also called a dwad, duad or dwadachamsha, is 1/12 of a zodiacal sign. The dwadasamsa was developed by Hindu astrologers who broke the 30 degree sign down into 12 equal parts of 2.5 degrees each. It is based upon the principle of the part being a reflection of the whole, and 12 signs of the zodiac were placed within the confines of one sign. It is believed that these signs within a sign, by virtue of their planetary rulers, account for subtle shadings of expression found in different degrees of that sign. Therefore, in addition to the sign having a primary planetary ruler, it would also have a sub-ruler, based upon which dwadasamsa it is placed in.