Apparent B-mag bt corrected for galactic extinction, ag , internal extinction, ai and k-correction ak . ... ak(-5)=0.15 . ... When unknown, v is assumed to be 0, i.e. no k-correction is applied, and when t is not known, a value of 2 (mean morphological type in the database; spiral galaxy) is assumed. ai is taken as 0 when unknown. btc is not computed when 30000 km/s or bt or ag is unknown. HyperLeda . ...