This article describes how to go from a crosstab...
..to an output displaying the difference between columns:
Requirements
A table with multiple rows and columns and a single statistic.
Method
1. Select your table.
2. Copy the name from General > General > Name
3. Select Calculation > Custom Code.
4. In the R Code editor, add a line that subtracts the first column of the table from the second column using the table_name[row,column] reference format:
diff = table.preference.by.wave[,2] - table.preference.by.wave[,1]
5. [OPTIONAL] Alternatively, you can first define the table to make the formula tidier and even add the original table columns to the 'difference' column:
tab = table.preference.by.wave
diff = tab[,2] - tab[,1]
diff.table = cbind(tab,Difference=diff)