1971    -999    -999   -13.9   -17.2   -20.2   -20.3   -23.6   -23.5   -23.5   -19.0   -15.1    -7.2
1972    -4.0    -8.5   -14.0   -15.8   -22.5   -22.2   -22.4   -25.7   -23.7   -22.7   -15.2    -6.8
1973    -5.7   -11.4   -15.6   -18.7   -21.3   -23.1   -23.7   -24.8   -25.0   -22.4   -11.9    -8.7
1974    -6.5   -10.9   -14.5   -20.3   -21.6   -19.0   -27.7   -24.7   -23.8   -21.6   -12.9    -6.9
1975    -6.2    -9.3   -14.0   -19.4   -22.6   -25.0   -22.5   -27.4   -25.6   -22.5   -14.0    -7.6
1976    -5.7    -9.0   -15.1   -23.2   -23.1   -26.9   -25.9   -24.5   -26.1   -26.0   -13.6    -5.3
1977    -4.8    -9.0   -14.4   -18.6   -24.5   -23.7   -27.1   -24.0   -26.5   -20.7   -13.2    -7.2
1978    -7.5    -8.4   -11.6   -16.2   -23.5   -26.2   -21.7   -28.2   -25.7   -21.3   -12.8    -8.9
1979    -6.5    -9.3   -12.6   -15.8   -21.6   -23.0   -28.1   -25.2   -22.3   -20.0   -12.5    -5.2
1980    -6.0    -8.4   -10.3   -15.4   -18.7   -24.8   -24.9   -23.9   -21.2   -23.6   -11.5    -7.4
1981    -7.6    -7.9   -12.5   -16.5   -20.6   -21.2   -23.2   -22.1   -22.1   -18.8   -14.5    -8.1
1982    -6.8    -8.1   -15.1   -21.0   -20.5   -20.7   -25.3   -26.7   -24.3   -20.3   -12.8    -6.1
1983    -5.2    -6.4   -12.4   -17.2   -18.7   -23.6   -27.7   -28.8   -21.2   -21.5   -14.7    -6.6
1984    -5.8   -10.0   -13.6   -19.1   -20.0   -26.9   -29.9   -23.5   -22.4   -18.4   -14.6    -7.4
1985    -6.3    -9.1   -13.7   -17.9   -22.6   -24.3   -26.5   -26.3   -25.7   -22.8   -14.2    -8.2
1986    -6.2    -9.4   -10.7   -17.0   -19.8   -20.6   -24.0   -25.0   -26.3   -20.9   -14.2    -9.0
1987    -6.3    -7.9   -11.0   -16.6   -22.5   -20.0   -21.7   -25.0   -23.6   -18.8   -14.2    -8.5
1988    -6.6    -8.7   -13.7   -17.7   -23.6   -23.9   -25.5   -26.5   -20.7   -18.6   -13.1    -7.2
1989    -7.5   -10.3   -13.2   -18.0   -24.3   -28.7   -25.0   -27.5   -21.6   -19.9   -13.7    -6.8
1990    -6.0    -9.9   -14.2   -20.6   -19.3   -25.9   -19.3   -27.0   -26.9   -20.9   -13.3    -7.2
1991    -6.5    -8.9    -999    -999    -999    -999    -999    -999    -999    -999    -999    -999