The calculation starts by calculating the electrical field in space for a radio signal of a given frequency, normally traveling along the "X" axis in three-dimensional space. This field is uniform in "Y" and "Z", but varies along the "X" axis; the signal's magnitude at any point along "X" is defined by the phase at that instant. Antennas work because the field changes over time as the wavefront moves past the antenna. This changing field induces current in conductors, the voltage being defined by the magnitude of the field at that instant. An antenna consists of extended but finite length conductors, so the pattern of the field results in different voltages at different points around the antenna. In antenna terms, each of the conductors making up the antenna is known as an "element".