入 針 出 針 之 法  law of time of insertion and withdrawal of 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.

八 十 難 80th difficult issue
Bā shí nán
論 入 針 出 針 之 法 law of insertion and withdrawal of needle
Lùn rù zhēn chū zhēn zhī fǎ
八 十 難 曰 ： 80th difficult issue says
Bāshí nán yuē:
經 言 ： tretises say
Jīng yán
有 見 如 入 ， there is a sighns when to insert needle
Yǒu jiàn rú rù
有 見 如 出  者 ， and there are signs of withdrawal of needle
Yǒu jiàn rú chū' zhě
何 謂 也？ 然 ： how to explain that? explanation
Héwèi yě? Rán:
所 謂 有 見 如 入 者 ， they say that there is a sign to insert needle
Suǒ wèi yǒu jiàn rú rù zhě
謂 左 手 見 氣 來 至 乃 內 針 ， it means that with left hand practitioner fells arrivel of qi and then he inserts the needle
Wèi zuǒ shǒu jiàn qì lái zhì nǎi nèi zhēn
針 入見 氣 盡 乃 出 針 ，when is a sign that qi is exhausted so he removes the needle
Zhēn rù jiàn qì jǐn nǎi chū zhēn
是 謂 有 見 如 入 ， they are signs of insertion
Shì wèi yǒu jiàn rú rù
有 見 如 出 也 。and signs of withdrawal.
Yǒu jiàn rú chū yě
to edit.