Partial sums pivot table

[#1]

Hello everyone,

I have a pivot table like this showing people going from one telco operator to another one.

RECEIVERS/GIVERS	ORANGE	VODAFONE	SFR	Totals outgoing
ORANGE	-	5	3	8
VODAFONE	2	-	4	6
SFR	5	6	-	11
Totals incoming	7	11	7	25

When I have the same operator, I have a '-' in my table which is normal but i would like to show instead of the ' - ', the balance : Incoming - Outgoing.

I would like to have this :

RECEIVERS/GIVERS	ORANGE	VODAFONE	SFR	Totals outgoing
ORANGE	- 1	5	3	8
VODAFONE	2	5	4	6
SFR	5	6	-4	11
Totals incoming	7	11	7	25

How can I do that please ?

For information, in my database I have something like this :

ID	RECEIVERS	GIVERS
1	ORANGE	SFR
2	ORANGE	VODAPHONE
3	VODAFONE	SFR

..

Thanks for you help