Herbs in the system are classified by their ability to either build or tonify (+), react amphoterically (which means to stabilize or harmonize) (0), or to eliminate (-). Herbs on the apex of each triangle represented the "king", the ruler/significant herb/neutral signified by a circle. A "minister", the herb that communicates to other plants and takes the message to the king, is signified by a plus sign. A "servant", the reciprocal part of the formula that acts upon/eliminates through the "doorways of the body". Measurement of herb was formulated by energetic strength, not weight, with the most potent herbs being used less than the milder ones.