From 1927–1929, Harlow Shapley and Helen Sawyer Hogg began categorizing clusters according to the degree of concentration the system has toward the core using this scale.
Mauthausen-Gusen concentration camp | Auschwitz concentration camp | Dachau concentration camp | Bergen-Belsen concentration camp | Sachsenhausen concentration camp | Ravensbrück concentration camp | Gym Class Heroes | Tom Sawyer | Buchenwald concentration camp | Sawyer Brown | class action | Stutthof concentration camp | class | Jasenovac concentration camp | Grini concentration camp | Theresienstadt concentration camp | Robert J. Sawyer | Class A | working class | The Adventures of Tom Sawyer | Pam Sawyer | Flossenbürg concentration camp | DB Class 218 | Class War | British Rail Class 37 | Social class | Neuengamme concentration camp | British Rail Class 47 | Victorian Railways X class | GWR 3031 Class |