Surface reference mark Dreifaltigkeitsberg, used in 1875 for <a href="https://en.wikipedia.org/wiki/Grade_measurement" class="extiw" title="en:Grade measurement">Grade measurement</a> Spaichingen, district Tuttlingen, Baden-Württemberg, Germany
<a href="//commons.wikimedia.org/wiki/User:DKrieger" title="User:DKrieger">DKrieger</a>
CC BY-SA 4.0
<span class="int-own-work" lang="en">Own work</span>