1972  241.38  242.80  242.90  244.10  244.80
      1973  244.60  247.50  249.00  249.40  249.80
      1974  242.30  245.00  245.20  245.90  247.80
      1975  246.00  247.50  247.90  248.00  248.40
      1976  236.00  239.80  239.90  241.40  242.30
      1977  242.70  244.20  244.20  244.50  245.10
      1978  239.00  239.80  240.20  240.20  240.60
      1979  237.40  238.20  238.50  239.80  240.00
      1980  232.47  236.70  236.80  236.90  237.40
      1981  237.78  238.29  238.70  238.89  239.67
      1982  234.23  236.14  236.50  237.05  237.48
      1983  237.12  239.31  240.12  240.30  240.62
      1984  236.63  236.65  237.22  237.72  238.10
      1985  237.24  237.73  238.40  239.28  239.88
      1986  236.70  239.45  239.62  239.84  241.57
      1987  238.56  238.67  239.06  239.27  239.90
      1988  233.96  238.92  240.24  240.30  240.46
      1989  239.23  240.89  242.08  243.13  243.15
      1990  238.69  242.53  242.69  243.07  243.14
      1991  239.16  240.00  240.83  242.21  242.58
      1992  235.30  236.91  237.08  237.92  238.71