A moon figure - one perfect circle with the appended segment of a circle, two tiny circle in the face, two rods supporting the segment - this is the construction title Error on Green. But the title conveys more than the solution of a mathematical problem - "on green" is clear enough, but "error"? Inside one of the girl's round eyes is a crescent moon, inside the other eye a black sun from which rays are directed backward. Next to this eye are two overlapping rectangles, the one in front with a black teardrop. Tears turn up frequently in Klee.

Strangely enough, the moon disk cannot possibly be supported by the blue-green segment with the hands; it should fall forward. Is the ladder supplying the countervailing force? In any case, there is an "error" of balance - and "error" as well in the implied acrobatic anecdote. But would this suffice to bring tears? Perhaps the sadness comes from some remoter cause. Note that the lines of the nose terminate in antennae, the red line at the right disappearing in space, the black one at the left racing to infinity in a sweeping curve. This looks like some sort of remote control and bring to mind cosmic unity. The spirits that live beyond our planet are not all good spirits; have evil ones brought about the "error" which wrings a tear from the moon face?

Here everything proceeds according to law, i.e., the structure and articulation are governed by self-decreed rules. This is why the nose is shifted left of center, to make room for the rectangle at the right.