This article describes how to go from a standard table...
...to a table with an additional row that computes the difference between specified rows:
A table with multiple rows.
1. Select your table.
2. Go to Properties > RULES on the object inspector.
3. To apply the rule, select the Plus (+) > Table Computations > Difference Between a Pair of Rows.
4. OPTIONAL: Select the Statistic to use (if different from the default).
5. By default, it is set to choosing selections by Label but this can be changed to Row Position. The latter option allows you to choose specific rows based on the first row (for benchmarking) and the position from the end (for dynamic referencing). This ensures, for example, the last 2 rows are always used, even when a further row is added to the end.
6. Select the row under Row 1 to compute the difference from.
7. Select the row under Row 2 to compare against.
8. OPTIONAL: Untick Label new row automatically and enter new label.
9. OPTIONAL: Tick Replace table with difference to only show this new row.
10. Choose whether to show blank cells as blank or NaN.
11. Press OK.
This rule calculates then the difference between these two rows and displays it beneath the second row. Note, this rule can only apply to a single statistic and no significance tests are conducted on these cells. It is also not compatible with tables that have row spans.
Note, if you select Switch rows and columns on your table, the rule will no longer work due to the table dimensions changing. In this case, you will have to apply the Difference Between a Pair of Columns rule instead.