Pivot trouble (1 Viewer)

[Anakardian]

I have a problem with a pivot table that I am sure can be solved.

What i need to do is rather simple if it did not have to be done in a pivot.
My data is arranged and shown like this:
Date Hours MaxHours
03-11-13 740 792
01-12-13 674 672
01-01-14 568 744

What I need it to do is a new column with the formula Hours/MaxHours.
The problem is that hours and MaxHours as shown as the difference from previous.
The real numbers are rather different.

I would expect the following result:
Date Hours MaxHours Utilisation
03-11-13 740 792 0,93
01-12-13 674 672 1,00
01-01-14 568 744 0,76

I guess I need to use a calculated field however I have no idea how to make it take the difference from the previous value in a calculated field.

Thanks for your help

Anakardian