The depth dimension pointing into the body, describing how deep the field reaches. Readings are taken on horizontal planes at set depths along it, and every one of those heights is measured from the same starting point. That starting point is z=0: the face of a disc, the top surface of a mat, and the center of the tubing on a loop. A plane at 5 cm sits 5 cm above z=0, not 5 cm above the plane below it.
Also known as: Z Plane, Measurement Surface
The field is measured on a grid. Starting at the center, the test engineer steps a probe outward along each axis at a fixed point spacing, taking a reading at every point, and continues a little past the accessory edge to catch the field as it fades. The origin is the center of the accessory surface.
