The most familiar form of this striking illusion is made with arrow heads, thus
In attempting to compare the two horizontal lines one is confused so as to regard the line with outward-extending obliques longer than that with inward-extending obliques, though, measured from point to point, they are equal. The same illusion occurs in a variety of similar figures, such as
where the main lines are not drawn, but the distances from point to point are to be compared; or such as
where the two distances between points are again to be compared. Angles, however, are not necessary to give the illusion, as can be seen in this figure
or in this
