measures the monotonic relationship between two variables and is used in this study to assess the correlation between prediction errors and their associated uncertainties (standard deviations). A strong positive correlation (ρ close to 1) is desirable, as it reflects that higher uncertainties correspond to higher prediction errors, indicating that the model is effectively aware of its limitations. Figure (b) illustrates how ρ quantifies the relationship between ranks of errors and uncertainties, providing a robust global assessment of uncertainty quality that is unaffected by scale or distribution. This metric is particularly valuable for comparing UQ models across different datasets, as it ensures a consistent evaluation of their ability to capture meaningful uncertainty estimates.