Tidal height curves delivered by a chart plotter are among the most useful advances in recent years. Like all beautiful gardens, however, this one harbours a serpent, especially when you’re cruising on the continent. Some plotters have a clear menu system for defining the time they are using. Others do not, and to add to the confusion, on US-built units, terms such as ‘standard time’ do not always mean what the British-trained navigator imagines. For all we know, the plotter may never have heard of zone time, and two hours’ discrepancy on the sill of a Breton marina with a 9-metre rise can be terminal. The safest answer is to check the plotter’s curve against a paper tide table at the beginning of the season, note the time difference, and stick with it.