1930s & 1940s

6

6

10

12

4	6	6	6
6	6	8	10

1960s

4	4	4	6
6	6	6	6
6	6	6	6
6	8	8	8
8	10	10	10

1970s

6

8

8

10

1980s - 1990s and Beyond

4	4	6	6
6	6	6	10