SED of the Crab Nebula centred on the X-ray energy range. The best-fitting model (blue line, see details on the fitting procedure in Sect. 4 and Table 4) is shown along with measurements from different X-ray observatories. The normalisation of the spectrum measured with XMM-Newton (yellow band) has been scaled up by 16% to be consistent with the absolute flux measurement with NuSTAR (magenta band). The COMPTEL gamma-ray flux has been scaled up by 30% to match the extrapolation of the SPI spectrum.