Metaphysical Third Eye is the main practice in Metaphysical Taoism. It is a biological form of clairvoyance that can be trained and tested for consistency and accuracy. Unlike psychic Third Eye, which opens up the Third Eye chakra in meditation, Meta Third Eye trains the seer to read chi, energy streams and auras emanating from things all around us, and coming sometimes from great distances.
In mainland China, it is practiced in secret sessions and few will acknowledge it at present. like other metaphysical religions, metaphysical taoism studies the hidden world, the reality behind reality. All things are made of chi energy (from the tao te ching ch. 42), so one way to do the hidden word is with training to read chi. with this form of clairvoyance, one can identify invisible things, determine if someone is telling the truth, if someone is in love, if food has been poisoned,etc. there is rumors that the chinese military may studying this practice too.
there is only article about metaphysical third eye in english online, and it was written with the help of a practitioner of this art. the article is linked below. go to the last section of the article (section d) to see the simple exercises for developing the basic skillset.
taocurrents.org/2014/12/29/metaphysical-third-eye-a-beginning-class/
This picture is a modified dao-yin image to illustrate how it works. Besides the exercises, the article explains the Taoist principles behind how it works. The chi is absorbed into the skin (hand in the image) and then processed in the body.