Arabic calligraphic tracing by Maaz Jan, based on a land surveyor diagram by Eltje Jacob Eltjens in his Leerboek Landmeetkunde (1750).
The diagram, drawn on a tracing paper, shows a tree, a small tower, another tree and a large tower, all drawn in black ink. From the bottom of the small tower and the trees, lines in red ink go to the top of the large tower. Together they form a triangle. The end of each line is marked with arabic letters.