- = Distance between the galaxy centers
- = Diameter of the galaxies involved.
The catalog contains galaxies up to a magnitude of 16, but is only complete up to a magnitude of 14.5.
Approximately 40% of the catalog data are misinterpretations, i.e. weak stars were wrongly classified as galaxies due to the insufficient quality of the photo plates used at the time . Nevertheless, the catalog is regarded as the beginning of double galaxy research. The galaxy pairs or multiple systems from the catalog are cited as spar plus consecutive catalog number. For example, Holm 427 is the pair of NGC 4567 and NGC 4568, also known as NGC 4567/8 . Holm 820 is the galaxy trio consisting of NGC 7769 , NGC 7770 and NGC 7771 .
- E. Holmberg: "A study of double and multiple galaxies together with inquiries into some general metagalactic problems: With an appendix containing a catalog of 827 double and multiple galaxies", Annals of the Observatory of Lund, Volume 6 (1937)
- A. A, Mikhailov (Ed.): Physics of Stars and Stellar Systems , Moscow 1962, §188 Double and multiple galaxies , translated into English by Z. Lerman, Israel Program for Scientific Translations, Jerusalem 1969
- W. Eichendorf, M. Reinhardt: Doppelgalaxien , Westdeutscher Verlag 1981, ISBN, 978-3-322-98861-4, page 3