The zero ohm coil (ZOC) is a special form of transformer core coil. This is also made of the top quality material FERON described in the chapter "Transformer Core Coils". In the ZOC, an air gap is calibrated and adjusted by hand between the two laminated cores (one I-shaped and one E-shaped). The air gap determines the inductivity of the coil and demands great care in the manufacturing process. It must not be too small, as saturation effects would otherwise occur at high loadings. The high production costs of the ZOC, and thus its higher price, are always justified when maximum faithfulness in pulse reproduction is required.