This image was acquired from
wikimedia. It was marked as Public Domain or CC0 and is free to use. To verify, go to the source and check the information there.
NHP Berlin Sternwarte Schnitt Scalastein Tafel VII. en Mean sea level benchmark vertical section de Normalhhenpunkt Vertikalschnitt Scan from book Trigonometrische Abteilung der Landesaufnahme PDold Normalhhenpunkt Levelling
Page 2023 Free-images.com. All images are Public Domain