The GCA (Ground Controlled Approach), or more specifically PAR (Precision Approach Radar), until recently was the main precision approach procedure used by military; in some cases used by civilian flights as well. It consists of a radar controller that gives you continuosly azimuth and vertical path deviations indications toward the runway. It's considered almost reliable as an ILS of Cat.1, which means it's capable of drive you to the Runway with visibility down to ~600 mt and vertical visibility of 2~300 feet.
-= This version is for altitude in meters and alt. setting in mmHg =-