Your table might look something like this:
| Year | Quadrillion Btu | Year | Quadrillion Btu | |
1981 |
1.5 |
1991 |
3.2 |
|
1982 |
1.7 |
1992 |
3.3 |
|
1983 |
2.1 |
1993 |
3.4 |
|
1984 |
2.2 |
1994 |
3.6 |
|
1985 |
2.3 |
1995 |
3.8 |
|
1986 |
2.4 |
1996 |
4.0 |
|
1987 |
2.5 |
1997 |
4.2 |
|
1988 |
2.7 |
1998 |
4.5 |
|
1989 |
2.9 |
1999 |
4.6 |
|
1990 |
3.1 |
2000 |
4.7 |
Note that we have split the table in two parts to conserve space. The first and third columns represent the independent variable, time, and the second and fourth represent the dependent variable, consumption.
To answer a question about the year something happened, you can just read the table backwards, or you could actually construct the inverse function by interchanging columns. Either way, it is clear that consumption passed 3 quadrillion Btu's in 1990 — if we assume that the cumulative yearly figures are determined at the end of each year. Of course, this was just as clear from the graph in Figure 3.