Ratio between theory predictions for the isolated-photon differential cross section and measurements for ATLAS~, CMS~, and ALICE. Theory predictions are obtained for ATLAS with NNLOJET~ NNLO NNPDF3.1 PDFs~, for CMS with JETPHOX NLO and NNPDF3.0 PDFs~, and for ALICE with JETPHOX NLO and NNPDF4.0 PDFs~. Experimental uncertainties are shown here on the points centred at unity, for CMS and ATLAS statistical and systematic uncertainties are added in quadrature and shown as a vertical error bar. ALICE error bars are statistical uncertainties and boxes are systematic uncertainties. The coloured boxes centred at the ratio indicate the theoretical uncertainty on the PDF and scales. The luminosity normalisation uncertainty of each experiment is presented as an overall box around unity at the right of the figure centred at unity.