obs   date          dt   error
2  1974.93 -0.11412003 0.06048
3  1976.13  0.02017998 0.20736
4  1976.93 -0.28405002 0.05184
5  1977.58 -0.44069999 0.04320
6  1977.96 -0.46414001 0.02592
7  1978.23 -0.60691001 0.02592
8  1978.42 -0.56348002 0.06048
9  1978.82 -0.76762003 0.04320
10 1979.31 -0.96714002 0.02592
11 1980.10 -1.22854003 0.02592
12 1980.59 -1.45820999 0.07776
13 1980.59 -1.44239998 0.02592
14 1981.14 -1.75293997 0.01728