Observing the Pressure
AG2 Ferguson has some guidance for you as you make your pressure observations.
AG2 Ferguson: "Sea level pressure is determined by reading the station pressure from the shipboard barometer and adding the appropriate additive reduction constant to your elevation on the ship. The station pressure can also be used to compute the pressure altitude, or PA, and density altitude, or DA. Pressure altitude is reported in feet and represents the height above or below sea level the given pressure would occur based on standard atmosphere. The density altitude is the height above or below sea level that a given density would occur."