Selecting Two or More Values at Once (IOD 301)

A question asking for a single value off a table takes one lookup: find the row, find the column, read the number. A question asking for a difference, sum, or ratio between two values takes that same lookup done twice, plus a step of arithmetic, plus a step of checking you grabbed the right two numbers in the first place. That is roughly four times the work, not twice, because every extra value is another chance to misread a label or grab the wrong row.

The fix is to read one value, write it down next to its label, then go back to the source and read the second value the same way. Don't try to hold both numbers in your head while your eyes jump around the graph or table. Label each number as you pull it: '70C → this kPa', '30C → that kPa'. Once both are written with their labels attached, the subtraction or comparison is just arithmetic. For a curve reading 1.2 atm at 10C and 3.6 atm at 50C, the pressure difference is 3.6 minus 1.2, which is 2.4 atm.

This connects directly to trend-reading and translating between tables: once you can pull two labeled values cleanly, you can check whether a pattern holds, convert a described relationship into numbers, or hunt across two different tables that use different row labels. In that last case, match the groups by name or condition, not by position in the table, since Table 2's rows may be ordered differently from Table 1's.