PIVOT - Show values as Difference From

If I understand correctly then:
1. Drag SL% down to the Values area again and change the "Show values as" to Difference from > week > previous (Number format > percentage)
2. [Optional] Change the column header of the new columns to read: Diff from previous week
As to the 2nd problem, when I started to produce another pivot table the original one suddenly showed the values in the "Sum of SL %" columns (I don't know why that happened).
Let us know if you have any questions.