**Determining the Upper Critical Magnetic Field for N-Doped Lutetium Hydride Directly from the Source Data Files in Dasenbrock-Gammon et al., Nature 615, 244 (2023)**, D. R. Harshman and A. T. Fiory [arXiv]

The Ginzburg-Landau-based upper critical magnetic field H_{C2} (0) ≈ 88 T for N-doped lutetium hydride, reported in Dasenbrock-Gammon et al., Nature **615**, 244 (2023), is obtained therein by modeling resistance behavior, defining transitions widths, and applying magnetic fields H = 1 T and 3 T. A method is presented herein for determining the critical temperature *T*_{C}(*H*) directly from the resistance drops in the source data, implying a temperature slope -d*H*_{C2}/d*T* of 0.46(6) − 0.51(5) T/K and, by applying pure BCS theory, an *H*_{C2}(0) of 71(10) − 79(8) T.

Dale R. Harshman and Anthony T. Fiory, arXiv:2305.12065 [cond-mat.supr-con] (2023).