Unit Years Exam Weight
Period 1 1491-1607 4-6%
Period 2 1607-1754 6-8%
Period 3 1754-1800 10-17%
Period 4 1800-1848 10-17%
Period 5 1844-1877 10-17%
Period 6 1865-1898 10-17%
Period 7 1890-1945 10-17%
Period 8 1945-1980 10-17%
Period 9 1980-Present 4-6%