Ferro meridian

The line of longitude running through El Hierro (Ferro), the westernmost of the Canary Islands, was known in European history as the prime meridian in common use outside of the future British Empire.

In 1634, France ruled by Louis XIII and Richelieu decided that Ferro's meridian should be used as the reference on maps, since this island was considered the most western position of the Old World.

[2] Flores Island lies further west, but the Azores were not discovered by Europeans until the early 15th century, and their identification as part of the Old World is uncertain.

But for the geodetic networks of Austria, Germany and Czechoslovakia, the value 17° 40ʹ 00ʺ was adopted in the 1920s, not only for practical reasons but also as it was discovered that the longitude of the Berlin (Rauenberg) fundamental point was miscalculated by 13.39ʺ.

The island of El Hierro spans more than a quarter of a degree of longitude,[3] from Ensenada de Juanil at 17° 52ʹ 59ʺ W to Roque del Guincho at 18° 9ʹ 41ʺ W.