Duomo fire is the vital heat of the gross vital form, the fire in the navel center. The three-finger is referring to the thickness of the subtle flame extending from the base of the spine going up through the top of the head and then down the frontal line. The spine is the conductivity of the vital energy. If we allow this conductivity we can intensify our vital energy. It is a practice of conductivity of the life-force to call up the duomo fire and maintain our body heat. When flowing this leads to greater vitality, energetic health and wellbeing.