These contain magnets that are within a coil, or coils, of copper wire. A wire wound coil is the secondary winding. Electromagnets usually consist of wire wound into a coil. Typically it consists of a wire wound into a coil or helix. It typically consists of a coil or helix of wire. The plug is connected to the high voltage generated by an ignition coil or magneto. Each cylinder has its own miniature ignition coil. Regulated designs compensate for the impedance of the transformer or coil. The temperature is regulated by heat input from electrical coil heaters. It is electrically similar to engines that have a coil pack. This is generally done by placing a resistor in series with the meter coil. The ejector is a plunger on the bolt face actuated by a coil spring. It consists of a tiny, powerful magnetic needle pivoted at the centre of the coil. Level shifts caused by resistive heating of the voice coil are termed power compression. In passive microphones, this value relates to the impedance of the coil (or similar mechanism).