Rhumb is the interface for instruments that sit between a person and a machine. It plots, annotates, and corrects on a luminous chart — the navigator's table, not the cockpit glass.
A rhumb line holds one bearing the whole way — a constant-angle course across the graticule. Rhumb the interface treats every reading the same way: the grid mediates, fixes mark the truth, and bearings are noted in the gutter, never stamped on the part.
That is the whole posture — pilot at a distance from the machine, reading state through a calm chart instead of a shouting dashboard.
Project position from course and speed alone. The plot advances even when nothing outside will answer.
Two bearings on one mark, advanced for the run between. Where the rhumb lines cross is the truth you act on.
The current carries the hull off the line. Read the offset, lay a new bearing, and the margin keeps the correction.