TINA/Spice: How to make a resistor value depends on other resistor?

Tool/software: TINA-TI or Spice Models

Hi, 

I am simulating a circuit.

One resistor in the circuit depends on other resistor.

let's say R3 depends on R1.

R3 = R1 / 8

I tried to put R1 on the value field of R3 but there is a message that it is not a correct value.

I appreciate any suggestion.