The wire, which is constantly fed from a spool, is held between upper and lower diamond guides which is centered in a water nozzle head. The guides, usually CNC-controlled, move in the "x"–"y" plane. On most machines, the upper guide can also move independently in the "z"–"u"–"v" axis, giving rise to the ability to cut tapered and transitioning shapes (circle on the bottom, square at the top for example). The upper guide can control axis movements in the GCode standard, "x"–"y"–"u"–"v"–"i"–"j"–"k"–"l"–. This allows the wire-cut EDM to be programmed to cut very intricate and delicate shapes.