The magnitude of the OR across the test set varies between O(1) -O( 3 ) deg [dm (g mL)] -1 . In the plots, each ∆ ref i bar is color coded from blue to red with increasing magnitude of the reference OR value for each molecule. The change in color was restricted to a range of 0 to 100 deg [dm (g mL)] -1 , such that the bars for molecules with OR values exceeding 100 deg [dm (g mL)] -1 are displayed as the same color (red). This is done for ease of comparison as a few of the molecules, in particular the helicenes (45-49 in Figure ), exhibit very large OR values relative to the rest of the set. This approach is slightly altered in the experimental comparisons, where the maximal value for color coding is set to 500 deg [dm (g mL)] -1 to more easily distinguish the molecules in the given set. This color coding visually provides information about any possible correlation between the sign of the error and the magnitude of the OR. Note that, although relative errors tend to be larger for molecules with small-magnitude OR, this is not a major issue for the data and it becomes less significant as the basis set size increases. On the other hand, using a single definition of the error as in Eq. 9 (plus the color coding) allows us to treat the entire test set on the same footing. It also allows us to combine information about the distribution of errors into a single plot.