Reading Register operand Quntinty from one Rate to other rate in Same Billing Schema

Hello ,

I have two register which read Import and Export Consumption .Both register reads are coming from Seperate Rates(Rate 1and rate2) through register operand  in Same Billing Schema.I want to do dedect Quantity from  rate1 to Quantity from rate2 but i am not able to do this my rate steps.Please help me if anybody knows solution.

Thanks,

LN