Even in the age of high-speed internet at sea, remarkable weather model forecasts, and satellite wind measurements, our knowledge of the correct atmospheric pressure, and how it changes with time, remains the key to safe, efficient routing decisions. Pressure data are also the most direct means of evaluating the model forecasts that we ultimately rely on for routing. Productive barometer use in navigation is a relatively new concept — it was actually used more effectively in the 1700s than in the 1900s. The Barometer Handbook explains its interesting history and its role in marine navigation. The major change came when accurate, affordable…