| 年度 | 实际值 |
|---|---|
| 1949 | 20 |
| 1950 | 20 |
| 1951 | 20 |
| 1952 | 20 |
| 1953 | 20 |
| 1954 | 20 |
| 1955 | 20 |
| 1956 | 15 |
| 1957 | 15 |
| 1958 | 14 |
| 1959 | 14 |
| 1960 | 12 |
| 1961 | 12 |
| 1962 | 12 |
| 1963 | 12 |
| 1964 | 10 |
| 1965 | 10 |
| 1966 | 10 |
| 1967 | 10 |
| 1968 | 10 |
| 1969 | 10 |
| 1970 | 10 |
| 1971 | 10 |
| 1972 | 10 |
| 1973 | 10 |
| 1974 | 10 |
| 1975 | 10 |
| 1976 | 10 |
| 1977 | 10 |
| 1978 | 10 |
| 1979 | 10 |
| 1980 | 11 |
| 1981 | 12 |
| 1982 | 12 |
| 1983 | 12 |
| 1984 | 12 |
| 1985 | 12 |
| 1986 | 12 |
| 1987 | 12 |
| 1988 | 12 |
| 1989 | 12 |
| 1990 | 12 |
| 1991 | 12 |
| 1992 | 14 |
| 1993 | 14 |
| 1994 | 14 |
| 1995 | 14 |
| 1996 | 14 |
| 1997 | 15 |
| 1998 | 16 |
| 1999 | 17 |
| 2000 | 16 |