I just checked mine and Hugh’s spectra from 23rd March in the Nova Cas 2021 thread. The graphed spectra are calibrated in wavelength with a linear X axis and the Balmer (and other line) wavelengths are correct and consistent between the two spectra
https://britastro.org/comment/10272#comment-10272
https://britastro.org/comment/10277#comment-10277
Mike’s spectrum image is not calibrated in wavelength.
https://britastro.org/comment/10242#comment-10242
Prism spectra are very non linear with the short wavelength end significantly stretched and the longer wavelengths compressed