How to assign output of a block to a variable during simulation?

Hi, i am stuck in a simple challenge! In my simulink model there is a Math operation product block which it's output determines the value of a variable resistor (R). the output of product changes continuously during simulation. So the question is how can i assign output of product to a variable called R which is changing continuously during simulation?

[I tried GOTO and From workspace but it seems that Simulink is not updating workspace variables in real-time and only does it at the end of the simulation]