Thermal pressure in the PDR of ONC disk as a function of the incident FUV radiation field G₀. The uncertainties on P_th arise from those associated with the length of the emitting layer, considered as the standard deviation of the IF radii, and from the uncertainty on the temperature of the HII region. The red squares are values for various PDRs reported by Joblin et al. (2018) and references therein. The dotted lines correspond to the relations obtained in the models of Bron et al. (2018), considering an O-star for the irradiating source. The dashed black line corresponds to the empirical relation obtained in Wu et al. (2018) for Trumpler 14 in the Carina Nebula. The dash-dotted orange line correspond to the analytical relation of Seo et al. (2019) (also discussed in Wolfire et al. 2022), using the values of θ¹ Ori C derived in Appendix H.