Parallel Index

Parallel indexing is a radar technique for monitoring a vessel’s position relative to a planned track by drawing one or more lines on the display parallel to the intended course at a set offset. As the ship runs along the track, a fixed, radar-conspicuous object (a headland, buoy, or light) should track down the parallel line; any drift off the line shows cross-track error to be corrected. It gives a continuous check on lateral position in confined or coastal waters without repeated fixing.