Mareograph for the recording of tides
The tide forecasts are calculated from a series of temporal data obtained from mareographs in previous years. This series of data is adapted by the method of least squares using Foreman's algorithm (Foreman, M.G.G., 1977. Manual for Tidal Heights Analysis and Prediction).
The greater the series of data obtained the greater the accuracy of the forecast, as we will have a greater number of harmonic constants. However, the implementation and gathering of data with mareographs are complex processes, and given that normally there is little variation in tides for relatively close locations, it is possible to forecast the tides of the secondary ports (those for which the harmonic constants are not available) making some simple corrections in the times and heights of the reference ports (for which we have obtained a long series of reliable sea level data).
The party responsible for siting and gathering the data for the mareographs is the government of each country, publishing the latest forecast made in the tide yearbook and also on occasion the latest harmonic constants obtained.