(data "Harvested Trees"
:about "In this experiment, the length of trees are mesured by two methods: Triangulation and Direct. Triangulation involves measuring the horizontal distance to the base of the tree, the elevated distance to the crown of the tree and the angle of the crown of the tree from horizontal are measured to compute the triangulated length of the tree. Then the trees are cut down and are measured in the ordinary way for the direct measurement. 

The question is are the two methods equal? The answer is no, triangulation generates a shorter distance, which is a benefit to the buyer of the tree (the logger).

This example was obtained by Louis Le Guelte from Dagnélie, Théorie et méthodes statistiques, Presses Agronomiques de Gembloux, vol. 2 p. 37-39, 449 PP., 1970."
:variables '("Direct" "Triangle" "Diff")
:data '(
20.4  21.7  -1.3
25.4  26.3  -0.9
25.6  26.8  -1.2
25.6  28.1  -2.5
26.6  26.2   0.4
28.6  27.3   1.3
28.7  29.5  -0.8
29.0  32.0  -3.0
29.8  30.9  -1.1
30.5  32.3  -1.8
30.9  32.3  -1.4
31.1  31.7  -0.6))
