Add calculated dimesion in a existed dimension field

[#1]

In a pivot tabel,  I want to add a calculated item like in a pivot table in excel.

Month	Area	Product	Qtty	Amount
ian.15	A	X	1	2
feb.15	A	Y	1	2
ian.15	B	X	1	2
apr.15	B	Y	1	2
mai.15	A	X	1	2
iun.15	B	Y	1	2
iul.15	C	X	1	2

calculated:  B vs A %

			Month
Product	Data	Area	ian.15	feb.15	apr.15	mai.15
X	Sum of Qtty	A	1			1
		B	1
		C
		= B/ A %	1	#DIV/0!	#DIV/0!	0

[Anonymous]

Maybe you can use partial sum instead, and expression will be

if(dimensionality()=2, sum(Qtty),
sum({<Area={B}>}Qtty)/sum({<Area={B}>}Qtty))

See attached