Given the interest in helical MOs as a means to understand related properties and the range of molecular systems in which these MOs appear, it is problematic that the assessment of helical MOs relies on visual inspection alone. It is thus altogether binary; if an MO is shaped like a coil we may deem it to be helical. This definition suffices to classify the trivial example shown in Figure because we can clearly see that the MO is shaped like a helix. However, we need a more stringent definition if we wish to deal with cases of varying degrees of helicality. Without a quantifiable measure of the degree of helicality of the MOs, it will not be possible to directly correlate them with observable molecular properties.