Braak Base Line
Heinrich Christian Schumacher had a good relationship with the Danish King Friedrich VI., which enabled him to set up the observatory in Altona near Hamburg, which was then in Denmark. His teacher in Göttingen was Carl Friedrich Gauss . So Schumacher initiated the Danish king's request to the Hanoverians to let Gauss participate in the measurement of the baseline. Both were on location from 12. September to 25. October 1820 to combine the surveys of both kingdoms across the Elbe river. Gauss was thus able to forego his own length measurement.