Qlikview Exression

[#1]

I am designing a bar chart with three expression. Could someone tell me how would i find the difference between two expression

expression1:sum({<
YTD_Flag_Fiscal = {'-1'},
_factTable = {'msData'},
TotalCalcs = {"$(=SubField(Concat(distinct TotalCalcs, '#'), '#', 1))"}
>} value)

expression2:sum({<
LY_YTD_Flag_Fiscal = {'-1'},
_factTable = {'msData'},
TotalCalcs = {"$(=SubField(Concat(distinct TotalCalcs, '#'), '#', 1))"}
>} value)

First expression computes a set of measures like sales, margin etc for 2014 and the second expression computes the same for 2015.

Need to have a third expression showing year on year change = (expression2 - expression1)/ expression 1.

I am unable to find the difference between the two expression using a '-' operator. Is there a diff function similer to a sum function.