Histogram distribution of best-fit parameters arising from Poisson statistics alone (in red, the 90% quantile is indicated with the gray area) and from Poisson statistics and calibration errors (in blue, the 90% quantile is delimited with the blue dashed line). Top-left: spin parameter. Top-right: height of the irradiating source. Bottom-left: power law index. Bottom-right: reflection fraction. The case simulated here corresponds to a spin of 0.5, a 1 mCrab source observed for 100 ks, with a reflection fraction set to two. As can be seen, at the level of calibration errors considered here, the spin parameter and the height of the X-ray source do not suffer from any significant systematic error, while the systematic errors on the power-law index and reflection fraction are larger, but remain small. No biases are introduced in all cases; see Sect. 5.