In the Hour System of Qi Men Dun Jia, every Yuan (元) in use is related to the 24 Seasons, the 10 Day Stems and the 12 Branches.
Each Season has 15 days in total, where 5 days each are allocated to each Yuan (元) – Upper Yuan 上元, Middle Yuan 中元 and Lower Yuan 下元.
Based on the Chinese calendar, 1 year has 24 Seasons, and thus 15 days x 24 Seasons = 360 days per year. Shortfall of approx 5.24 days (i.e. 365.24 days per year, as the Earth orbits around the Sun).
Each Season’s transition
day will not meet with the Lead Day 符頭, which is the first day of the Upper Yuan.
1) 節氣 and Upper Yuan Lead Day (符頭 Fu Tou) falls on the same day – which is Jia Zi 甲子 day, Ji Mao 己卯 day, Jia Wu 甲午 day, and Ji You 己酉 day – it is call ‘正授’
2) 符頭 Fu Tou is at the beginning of the 節氣, it is known as ‘超神’
3) 符頭 Fu Tou is towards the end of 節氣, it is refer to as ‘接氣’, this is the Qi Extension Method called 置潤.
置潤 is use to adjust the gap between Lead Stem 符頭 and the Seasons 節氣. Just like the lunar calendar has a principle of 潤月.
It is important to note that the Qi Extension Method or 置潤 only happens in specific Seasons, like Planting of Thorny Crops 芒種 and Greater Snow 大雪.
芒種 comes before 夏至 and is the last Season of 陽遁. 大雪 comes before 冬至, and it belongs to the last Season of the 陰遁.
冬至 is the starting point of the 陽遁
夏至 is the starting point of the 陰遁
The principle of 置潤 is to adjust the gap between 符頭 and 節氣 in this 2 period so that it transit smoothly from Yang to Yin / Yin to Yang.