Double-check that tide height

Electronic tidal height calculators such as those found on a good plotter are a huge bonus to the navigator. However, when a height is critical, it doesn’t always pay to rely on a single electronic source. It’s by no means unknown for two plotters to deliver somewhat different predictions for a secondary port at two-thirds flood, for example, and for both to vary from a steam-powered calculation using the Admiralty Tide Tables graph, ‘Mark One Brain’, and an honest pencil.