Theory

Station pressure and sea-level pressure

The pressure sensor measures the air pressure where the phone is sitting. That is station pressure. Because pressure decreases with height, weather observations are commonly reduced to a sea-level equivalent so values from different elevations can be compared. Marine Barometer uses calibrated station pressure and the selected reference elevation to produce the Barometer reading.

Why reference elevation matters

If the phone moves uphill while Marine Barometer still assumes the old elevation, the lower station pressure can look like a rapid weather-pressure fall. Moving downhill can look like a rise. Location, GPS and Manual Reference Elevation are three ways of telling the Barometer what elevation should be used for normal sea-level correction.

What Barometer Lock assumes

For a short excursion, Barometer Lock deliberately assumes that true weather pressure is essentially constant for up to 60 minutes. It captures the current Barometer value and holds it while the phone changes elevation. The Altimeter is initialized at the start so the movement can be seen as altitude instead of being mistaken for weather.

This is a short-trip convenience, not a way to measure real weather-pressure change while travelling for a long time.

Why the Altimeter needs a reference setting

An altimeter converts pressure into indicated altitude. The same atmospheric pressure can correspond to different indicated altitudes depending on the reference setting. QNH, QFE and QNE make that reference explicit rather than hiding it inside the calculation.

What pressure trend tells you

A rising barometer is often associated with improving or more settled weather; a falling barometer is often associated with deteriorating or unsettled weather. Rate and size of the change matter. Local weather, topography and movement of the phone still matter, so pressure trend is one useful observation rather than a complete forecast.

Why a Tide Clock is approximate

The principal lunar semidiurnal tide has a period of about 12 hours 25 minutes, which is why traditional tide clocks turn slightly more slowly than an ordinary 12-hour clock. Real local tides combine several astronomical constituents and are shaped by coastline, seabed and weather. A simple tide clock therefore represents phase, not an exact harmonic prediction.