All Indicator heads (NT920RAI) are electrically and mechanically identical (no master / slave distinction) which provides complete interchangeability and straightforward system expansion. Each Indicator head comprises a robust centre zero moving coil driving an illuminated white pointer against a black scale background graduated in 5° increments. Provision is also made for fixed and variable intensity red backlight scale illumination for night viewing. Standard RAI heads are suitable for wheelhouse (sheltered) panel mounting. External locations may be used (foot bracket or panel mount) when supplied with a Navitron Pod assembly (PM).