| Year | Value | | 2000 | 452 | | 1999 | 500 | | 1998 | 800 | | 1997 | 800 | | 1996 | 800 | | 1995 | 800 | | 1994 | 700 | | 1993 | 600 | | 1992 | 4,200 | | 1991 | 3,900 | | 1990 | 3,900 | | 1989 | 3,600 | | 1988 | 2,000 | | 1987 | 2,000 | | 1986 | 2,000 | | 1985 | 2,300 | | 1984 | 2,200 | | 1983 | 1,900 | | 1982 | 1,800 | | 1981 | 3,600 | | 1980 | 4,200 | | 1979 | 5,900 | | 1978 | 5,900 | | 1977 | 5,900 | | 1976 | 9,800 | | 1975 | 10,500 | | 1974 | 10,100 | | 1973 | 10,100 | | 1972 | 5,000 | | 1971 | 4,700 | | 1970 | 4,400 |
|