68% containment radius of the γ-ray emission from the Crab Nebula measured with the combined Fermi-LAT and H.E.S.S. data analysis. The error bars denote the 1σ statistical uncertainties and do not include systematic effects. For comparison, the red points show the extension measured with Fermi-LAT by Yeung & Horns (2019, 2021), whereas the purple point displays the extension previously measured with H.E.S.S. (Abdalla et al. 2020). In grey we show the systematic uncertainty of the H.E.S.S. and Fermi-LAT measurements, respectively (cf. Sects. 2.2 and 2.3). The bottom panel shows the square root of the TS value of the measured extension, which gives an indication of the (statistical) significance of the extension with respect to the null hypothesis of a point-like source.