The Chinese have used sundials since at least the 4th century BC. Equatorial dials have been found, dating to the Han dynasty, measuring the day into 100 parts, or K'o, each equal to 14 minutes 24 seconds of the modern day. Portable sundials were referred to in a manuscript of the late Chou dynasty. Additional information is provided by a 14th-century Chinese manuscript, which indicates that scaphe sundials existed in the 13th century. After the arrival of Europeans in the 16th century, horizontal dials were introduced. Post-16th-century sundials are of two main types, referred to in Joseph Needham's "Science and Civilization in China" as Type A and Type B. Type A is the Chinese descendant of the European horizontal folding sundial with a compass, string gnomon, and unequal hour gradients for measuring equal-hour intervals at one or more specific latitudes. This type often has a moon dial on the reverse side of the lid. Type B is the direct descendant in Chinese lineage from earlier Chou and Sung models. It is a portable folding sundial with a compass, adjustable inclining dial, and a scale for adjusting the degree of incline of the dial according to the season. The scale has twelve different notches for inclining the dial according to the chhi (fortnight) of the season, going from winter solstice to summer solstice. Each notch is used twice during the year, once in the cycle of rising inclination and once in the cycle of descending inclination. In this manner the dial maintains only moderate accuracy in measuring equal fixed hours according to the season. In summer the dial can also be used for travelling if the degree of inclination for each chhi is known. The dial can then be used as an equatorial sundial, according to the latitude of the locality, but not in winter since the angle of the sun is below the inclined dial and there is no provision for indicating winter hours on the reverse. The compasses on both types of sundial have the cardinal points and the characters of the Twelve Terrestrial Branches and the Ten Celestial Stems as well as seasonal references engraved in the chart of degrees of azimuth around the compass dial. They refer to the sexagenary cycle and were used for purposes of divination.