Figure 8: A typical screen within the quaternary probabilistic submenu,
showing the placement of the different options.
Typing ? will summon the menu.
The quaternary probability layout is similar to the trinary layout, with the noticeable difference that a large stereopair occupies the top half of the screen.
The probability contour map is three dimensional, so it is represented by plane sections through the simplex, or unit tetrahedron. The option u selects one family of planes, the option v selects a family whose members interpolate the first; between the two one can locate prospective minima more accurately.
Likewise, the tetrahedron may be represented in two ways. The first, sitting on its base, which is the default selection, may be chosen through the option O. The second alternative is to think of the tetrahedron suspended between a pair of opposite, mutually orthogonal edges; E gives the corresponding presentation.