Δχ² curves with black hole spin as the interesting parameter for our spectral fits to M33-X7. The left panel shows the case for a standard accretion disc model (KERRBB), while the right panel shows the case where there is a warm Comptonising material above the disc (THCOMP*KERRBB). We have included both the previous mass estimate of 15.65  M_⊙ (Orosz et al. 2007, magenta line) and the updated estimate of 11.4  M_⊙ (Ramachandran et al. 2022, green line). The dashed black horizontal line shows Δχ² = 2.7, indicating 90 % confidence for one interesting parameter.