Starting with the HOMO 2 and HOMO 3 of dimethyl-spiro [4.4]nonatetraene (blue and red in the top of Figure ), we see non-uniform helicality across the molecule. There is a linear increase/decrease evident in the cumulated sum across the center of the molecule, indicating helical orbitals, versus step-like behavior close to the methyl groups. This is hard to see by visual inspection of the MOs in the top left corner of Figure . Furthest away from the spiro-carbon the orbitals are more similar to the rectilinear MOs we see in the unsubstituted spiro [4.4]nonatetraene or, simply, cyclopentadiene (see Figure ). This is also reflected in the MAD shown in Table : Using the full dataset gives a MAD of 17 for both HOMO-2 and 18 for HOMO-3. On the other hand, if the data set is limited to the carbons directly adjacent to the spiro-carbon, we get a MAD of 3 for the HOMO-2 and 8