Advertisement for land surveying in Grou, Friesland. Carved by Syoerdt Aetesz Haeckema. Placed on the house of Sytske Gravius in 1655. Both were working on an ordnance survey of Friesland.





On the top is a right triangle with Dutch writing. It says: In A recht. AB, BC en CA doen 30. AB is 7 langer als AC. Vrage na elck side. Which translates as: In A right: AB, BC and CA total 30, AB is 7 longer than AC, how long is each side?





The surveyor bottom left is using a Hollandse Cirkel. This instrument was invented by Jan Pieterszoon Dou in 1612. It uses two pairs of visors which are perpindicular to each other. They are useful for plotting perpindicular angles.

To the left is a map of Friesland from the late 17th century that Haeckema and Gravius likely helped create.