In different coordinate systems tensor components have different values, for each tensor there is at least one special coordinate system in which all of the shear components (Txy, Txz, and Tyz) are zero. In this special coordinate system, the three axis directions are called principal directions and the three diagonal components, Txx, Tyy, and Tzz, are called the first, second, and third principal values respectively. Principal values are tensor properties that do not change with the coordinate system.
Select this option to activate the first, second, or third principal value.