Back in the old days, when coastal pilotage relied heavily on three-point compass fixes to generate cocked hats of varying sizes, it wasn’t an uncommon error to take a fix from the wrong landmark. A town with three churches, or serried ranks of headlands stretching into the distance, all had the ability to throw the unwary navigator off track. The temptation would be to guess which was which, gleaning as much information from the chart as you could. When it came to navigating ships, however, especially naval ships, guesswork simply wasn’t good enough.
Every time you took a fix, therefore, you would take at least four bearings; three for your known landmarks and one to ‘shoot up’ your next object. For example, there’s a distinctive spire on the chart, and…