| Year | Value | | 1999 | 1,300 | | 1998 | 28,200 | | 1997 | 10,500 | | 1996 | 17,100 | | 1995 | 24,800 | | 1994 | 26,600 | | 1993 | 20,500 | | 1992 | 26,100 | | 1991 | 56,000 | | 1990 | 56,000 | | 1989 | 53,300 | | 1988 | 63,000 | | 1987 | 60,900 | | 1986 | 55,300 | | 1985 | 50,700 | | 1984 | 48,700 | | 1983 | 61,000 | | 1982 | 54,800 | | 1981 | 36,600 | | 1980 | 36,300 | | 1979 | 52,000 | | 1978 | 40,000 | | 1977 | 11,000 | | 1976 | 11,000 | | 1975 | 10,000 | | 1974 | 10,000 |
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