Chart No. 1 · Q 122
Measured distance (measured mile)
Buoys & beacons
Pairs of transit beacons with a stated distance and course let vessels calibrate speed and log.
What it means
Two pairs of beacons form transits at each end of a measured distance; the chart quotes the distance and the course to steer (e.g. '1852 m 090°–270°'). Run between the transits at steady speed to calibrate your log.
Why it matters
Time the run both ways and average, to cancel the tidal stream. It is one of the few chart features meant for boat testing rather than hazard avoidance.