Difference between Column

[#1]

Hello, i'm new here, and i'm trying to get some experience in QVW.

So this my question:

I'm trying to make the Difference between columns, for now, i have a table that show me this...

CONTRATO	Período	out/14	nov/14	dez/14	jan/15
10465914	Soma de Tot. Créd.	1540	10260	1166	1648
	Soma de Qtde. Créd.	24	60	50	4
	Quantidade de Cartões	12	30	10	4

and i want to make this

CONTRATO	Período	out/14	Dif Out-Nov	nov/14	Dif Nov-Dez	dez/14	Dif Dez-Jan	jan/15
10465914	Soma de Tot. Créd.	1540	15%	10260	880%	1166	71%	1648
	Soma de Qtde. Créd.	24	40%	60	120%	50	1250%	4
	Quantidade de Cartões	12	40%	30	300%	10	250%	4

So basically i want to divide one month to the next one

I appreciate if someone can help me, and sorry about my english or something