Parameter probabilities for the polcap model applied to the low-luminosity observation of GX 304−1. Correlations for different parameters are shown in color as two-dimensional confidence maps, where dotted, dashed, and solid contours correspond to the 99%, 90%, and 68% confidence regions, respectively. Here “ΔC-Stat” represents the statistic change compared to the best fit. Side panels on the right show the one-dimensional parameter probabilities.