V. Prelog, et al, Helv. Chim. Acta, (1962), 45, 129.

The diagram is from the Prelog paper. Nonactin is meso-D; the other meso compound is C. There are two other racemates, A and B. Four nonactic acids of one chirality gives an enantiomer. Its mirror image arises from the other enantiomer of nonactic acid. Three of one enantiomer and one of the other will produce the same result. Although each of the cartoons above appears to have a plane of symmetry, remember that each "Ns" is handed. Think of it this way. Assume the rotation of each nonactic acid unit in all the structures above has a rotation of +x or -x. You are a beam of plane polarized light running around the 32-membered ring. What is the net optical rotation?

A(+) = +4x

A(-) = -4x

B(+) = +2x

B(-) = -2x

C = 0

D = 0