Van Giffen has drawn contour lines on his excavation plans so we're lucky to have the original mounds of dolmens D30 and D40. Both mounds had an elliptical outline. Ellipses have a special feature in common with right angled trianges: half the diagonal of the long axes has the same size as the hypotenuse of the triangle, which is formed when circling a rope around two poles (blue in the figure right). The mounds of D30 and D40 can be derived from triangles with right angle sides of resp. 3:4 and 1:2.
The proportion 1:2 in the hill of D40 calls to mind the proportion grid seen with some enlarged dolmens (see the page Dolmens with satelites). A likewise configuration counts for the palisade ring near Goseck - one of the oldest neolithic rings of Europe . This ring has been derived from a right angled triangle with the proporion 1:2 too. The construction has been setup at a right angle compared to the mound of D40.
In the figures below one of the contour lines is traced by a blue dotted line. With the palisade ring this is the ground plan off the inner ring. The best fitting ellipse is drawn red. The black dotted line can be seen as a rope used to encircle the ellipse. The green line on both right figures determines the north-south axe while the grid has been setup with a proportion 1:2 again. The grid of the left figure (the mound of D30) lies north-south by itself.
In general the mounds of the German territory are represented by circles. (It can be questioned if they are true circles.) Therefore it's striking, that the mound of Sprockhoff 340 has been drawn as an ellipse. Again an integral right angled triangle forms the basis of the setup. The proportion of the right angle sides is 8:15. The long axis has an azimuth of 133º, so that the grid is similar to that of D21 and D22 (see the page D13, D21 and D22).