logd25 is the decimal logarithm of the length the projected major axis of a galaxy at the isophotal level 25 mag/arcsec 2 in the B-band (this is the diameter of the galaxy if it is a disk). Many papers were devoted to the study of diameters and specially to the reduction to the standard system defined by the isophote at the brightness of 25 B mag/arcsec 2 . ... The shape of the galaxy at the same isophotal level (B=25 mag/arcsec 2 ) is defined in the parameter logr25 . ... HyperLeda . ...