Comparison of spectra for the Crab nebula. The spectra shown in red, green, and blue were derived with the reflected background method with HAP, ctools, and Gammapy, respectively. For the HAP analysis, we show the result of the power-law fit in addition. We compute upper limits (95% confidence level) for flux points with a statistical significance of less than two standard deviations. The published spectrum is taken from Aharonian et al. (2006a); it uses a power law with exponential cut-off as spectral model.