Year January December
1  1959  315.42   315.43
2  1960  316.27   316.03
3  1961  316.73   316.85
4  1962  317.78   317.53
5  1963  318.58   318.20
6  1964  319.41   318.55
7  1965  319.27   319.25
8  1966  320.46   320.87
9  1967  322.17   321.80
10 1968  322.40   322.74
11 1969  323.83   323.95
12 1970  324.89   324.96
13 1971  326.01   325.85
14 1972  326.60   327.39
15 1973  328.37   328.48
16 1974  329.18   329.41
17 1975  330.23   330.59
18 1976  331.58   331.52
19 1977  332.75   333.68
20 1978  334.80   334.78
21 1979  336.05   336.56
22 1980  337.84   338.04
23 1981  339.06   339.44
24 1982  340.57   340.32
25 1983  341.20   342.82
26 1984  343.52   344.04
27 1985  344.79   345.38
28 1986  346.11   346.72
29 1987  347.84   348.78
30 1988  350.25   351.18
31 1989  352.60   352.37
32 1990  353.50   354.07
33 1991  354.59   354.89
34 1992  355.88   355.33
35 1993  356.63   356.78
36 1994  358.34   359.05
37 1995  359.98   360.74
38 1996  362.09   362.38
39 1997  363.23   364.34