Tenn. Code Ann. § 66-6-102: Coordinates used

The plane coordinate values for a point on the earth's surface, used to express the geographic position or location of such point, must consist of two (2) distances expressed in United States survey feet and decimals of a foot when using the Tennessee Coordinate System of 1927, expressed in either United States survey feet and decimals of a foot or meters and decimals of a meter when using the Tennessee Coordinate System of 1983, and expressed in either International feet and decimals of a foot or meters and decimals of a meter when using the Tennessee State Plane Coordinate System. One (1) of these distances, to be known as the "East X-coordinate," must give the distance east of the Y axis; the other, to be known as the "North Y-coordinate," must give the distance north of the X axis. The Y axis of any zone must be parallel with the central meridian of that zone. The X axis of any zone must be at right angles to the central meridian of that zone.