Cascais Tide Gauge

It was the year 1882 that Cascais got an observatory for studying tides with an analog mechanism by Amédée Phillipe Borrel, a French watchmaker. Impressively, to this day the mechanism continues to function. In 1895, the Cascais Tide Gauge (“Marégrafo”) moved to its present location, on top of a natural rock formation, on the steadiest possible platform. “The tide gauge records have been kept with no interruptions for more than 120 years”, explains José Manuel Campos, of the state heritage agency, who is in charge of the Tide Gauge’s maintenance. Seven days per week, the analog system tracks tides and records data with a pen (of different colours, changed throughout the week) on a sheet of paper. The resulting graphic is known as a “maregrama” (“tidegram”). “In the old days, this was a full time job for someone”, Campos says. The Cascais tide gauge also defined the Portuguese Altimetric Datum (the zero-level elevation), used as a reference for measuring heights in Portugal. What this means is that if you climb to the highest point of neighbouring Sintra - 528 metres high -, that altitude was measured from this sea gauge. Out of the four analog sea gauges once in Europe (the others were in France, the Netherlands and Scotland), this is the only still operating, and open for visitors.