How operands for two rate registers get populated with their respective registers consumption value

Hi Friends,

I am trying to create Rate steps for two rate registers meter(on peak and off peak) using single RATE, please see the below table for RATE steps for both the registers,

R1_onpeak and R2_offpeak operand's category is quant and operand usage  is register, can anyone let me know how operand R1_onpeak and R2_offpeak get populated with their respective registers consumption value because I haven't seen anything which relate these operands to their respective registers, In case of single rate meter it obvious since only one register is there.

Variant            input operand            input operand               output operand

Quanti01         R1_onpeak                 R1_price                    R1_amount

Quanti01         R2-offpeak                  R2_price                    R2_amount

Many thanks

Veer