The Warring States period (15th-16th Century) gave rise to a method for telling time, whereby one day was divided up into 2-hour blocks represented by the 12 animal symbols used in the traditional Chinese zodiac (Rat, Ox, Tiger, Hare, Dragon, Serpent, Horse, Ram, Monkey, Bird, Dog, Boar). 12 midnight to 2 in the morning was the time of the Rat, 2 til 4 in the morning was the time of the Ox, and so on. However, with 2-hour blocks set as the smallest unit of time, arranging meetings was difficult, so 'joukoku' (上刻) and 'gekoku' (下刻) were added to divide time into 1-hour blocks. For example, '丑の上刻' (ushi no joukoku) would be used to indicate the time between 2 and 3 in the morning. As Japan entered the Edo period (17th-19th Century), when times needed to be given in more detail, the 2-hour blocks between zodiac symbols were further divided into three 40-minute sections called 'joukoku' (上刻), 'chuukoku' (中刻) and 'gekoku' (下刻). With this change, '丑の上刻' (ushi no joukoku) now referred to the time between 2 and 2:40 a.m.