Type II supernovae as a distance indicator Could someone explain in brief exactly how type II supernovae could be used as distance indicators? as in simply the formulae used and how they are employed? I know there are certain methods based on expansion velocity etc but the open supernova catalog ( https://sne.space/ ) gives the absolute and apparent mag for type II supernovae too, why would we then need to use methods dependent upon expansion velocity and other complications when we can simply calculate distance using $10^{m-M + 5}$?
The open supernova catalogue calculates absolute magnitudes from the observed apparent magnitude, luminosity distance and redshift decrements.  They note that they don't account for spectral energy distribution shape, so absolute magnitudes may be approximate if there is significant absorption by dust.
So the catalogue isn't recording a measured or modelled absolute magnitude derived independently of the distance, (which is required if the SN are used as standard candles), but a calculated absolute magnitude derived from the apparent magnitude and the redshift.