The photocatalytic system has categorical variables (variables that are divided into groups, often non-numerical such as the molecular structures) and continuous variables (a quantitative variable that can any value with a fixed range, e.g., concentrations). Five continuous variables were sequentially varied in the system, namely, concentrations of catalyst, photosensitiser, surfactant, reductant and buffer, while the performance was quantified with five figures of merit, namely, YieldCO ). Because the experiment time is fixed, YieldCO and QYCO must follow the same trends, as must as TONCO and TOFCO. Varying the catalyst concentration shows that lower catalyst concentrations allow observation of higher TOFCO (~86±8, 11±2, 2.5±0.1 min -1 at 0.01, 0.1, and 10 µM, respectively; Fig 3A ); a trend that is consistent with general observations in the literature. However, the high TON and TOF come at a cost of selectivity and product yield (25, 50 and 89% CO and 0.05, 0.07 and 1.5 µmol CO h -1 ), emphasising the importance of considering the system holistically rather than focusing on individual figures of merit.