One of the earliest surviving mathematical treatises from ancient Han China is the Book on Numbers and Computation, part of the Zhangjiashan Han bamboo texts dating from 202 to 186 BCE. It presents basic mathematics problems and solutions and was most likely a handbook for day-to-day business transactions or affairs of government administration. The book contains problems and solutions serving agricultural purposes, such as field measurements of area, proportional exchange rates for agricultural millet and rice, distribution by proportion, short width division, and excess and deficiency. Some of the problems found in the Book on Numbers and Computation appear in the later text Nine Chapters on the Mathematical Art from 179 CE, with five exact matches. However, unlike the Nine Chapters on the Mathematical Art, the Book on Numbers and Computation does not deal with problems involving right-angle triangles, square roots, cube roots, and matrix methods, which infers the significant advancements made in Chinese mathematics between the writings of these two texts. The The Arithmetical Classic of the Gnomon and the Circular Paths of Heaven, written in dialogue form and with regularly presented problems, is concerned with the application of mathematics to astrology. In one problem which sought to determine the height of the Sun from the Earth and the diameter of the Sun, Chen Zi instructed Rong Fang to wait until the shadow cast by the 8 chi tall gnomon is 6 chi, where one chi was equivalent to 33 cm. Thus, a 3-4-5 right-angle triangle was constructed where the base was 60,000 li, where one li was equal to 415 m, the hypotenuse leading towards the sun was 100,000 li, and the height of the sun was 80,000 li. Like the Nine Chapters on the Mathematical Art, the Arithmetical Art of the Gnomon and the Circular Paths of Heaven also provides a mathematical proof for the "Gougu Theorem", also known as the Pythagorean theorem in the West. The Nine Chapters on the Mathematical Art was the most groundbreaking of the three surviving Han treatises, as it is the first known book to feature negative numbers, preceding the Bakhshali manuscript of India by at least two hundred years. Although the decimal system existed in China since the Shang Dynasty, the earliest evidence of a decimal fraction is an inscription on a standard volume-measuring vessel dated 5 CE and used by the mathematician and astronomer Liu Xin. The Nine Chapters of the Mathematical Art also featured decimal fractions as a means to solve equations and represent measurements. Gaussian elimination, an algorithm used to solve linear equations, was also included in the Nine Chapters of the Mathematical Art.