Comparison between 0.5–2 keV fluxes measured from the 0.2–2.3 keV spectral fitting and from the 0.2–2.3 keV count rate (imaging) for sources with less than 10 net counts in the 0.2–5 keV band. The relative errors in the right panel are the ratio between the 1-σ upper and lower limits and the median value, thus the upper and lower limits are displayed in the ranges > 1 and < 1, respectively.