Pivot Table subtract one column with another

[Pasan]

Level	Permanent	Permanent	Contract	Contract
	Base	Total Rate	Base	Total Rate
L1	10	20	15	25
L2	12	24	14	28

Hi All, In the above pivot table I would like to subtract Total rate of permanent by total rate of contract for each level. So the answer for L1 should be 20-25=-5. How can I do that in Qliksense pivot table?

[Chanty4u]

Try this 

Sum({<Type={'Permanent'}>} [TotalRate]) - Sum({<Type={'Contract'}>} [TotalRate])

[Pasan]

Nope, this does not work for some reason. Thank you!