入 針 出 針 之 法 rules of needles insertion and withdrawal
Eightieth difficulty of Nanjing explains rule of insertion and time of withdrawal. This difficulty is linked with 78 th difficulty which explains moment of insertion:
先 以 左 手 first with left hand
壓 按 所 針 press and then insert the needle
榮 俞 之 處 ，in the place of point where is Rong
彈 而 努 之，release and pull the skin
爪 而 下 之 ，press with finger
其 氣 之 來 ，arrival of qi
如 動 脈 之 狀 ，condition as pulse movement
順 針 而 刺 之 ，hold needle and puncture
得 氣 因 推 而 內 之 ， obtain qi and push inside
Archaic acupuncture describes that what ever moment of insertion is, practitioner press the point of meridian, moving it horizontally, feeling pulsation like movement under his finger< and insert the needle.
Moment of removal is not relayed on left hand rule. Practitioner controls signs of pulse changes according the fifty yin and yang cycles and one hundred cuts of Rong 榮 and Wei 衛 circulation. So Ring or Wei qi stays in meridian for 14.4 minutes. So if puncture started from the start of the cut, so needle will stay for 14,4 minutes until change is palpated in pulse so practitioner removes the needle as rong circulation is changed for wei or wei is changed for rong. If puncture starts in the middle of the 14.4 minutes cycle, so it will last for 7 minutes until practitioner palpates rong and wei circulation's change in pulse, it is sign to remove the needle.
Difficulty 80 is linked with difficulties 69, 71 and 72 which explain way of palpation of arrival of qi. NanJIng do not have explanation regarding palpation of exhaustion of qi in the point. It actually is not mentioned that practitioner with his left hand should palpate qi exhaustion. Meanwhile difficulty 1 of Nanjing explains how long qi as Rong or Wei qi stays in the point. Rong and Wei change of circulation is shown in the pulse, so practitioner of archaic acupuncture removes needle when Rong is exhausted in particular area and insert needle into wei and vice versa as indicated by pulse.