This includes defining the class well enough that members can be recognized, and finding enough members of that class with well-known distances to allow their true absolute magnitude to be determined with enough accuracy.
Dette omfatter at klassen skal være defineret så præcist, at medlemmer af den kan identificeres, og at finde nok medlemmer af klassen med en kendt afstand, således at deres sande absolutte størrelsesklasse kan findes med tilstrækkelig nøjagtighed.