Shunt Resistor for attiny85

I have performed all tutorials on the arm(STM32F3) controller and they are successful,

now I want to perform it on a different controller,
I have set there is shunt resistor connected in STM32F3 target board, Also got notduino has shunt resistor.
my question is, how to choose shunt resistor,
as I see in both (STM32F3 and noduino), there is two resistor connected,

STM32F3: 1R is connected to VDDA and 1R+12R is connected to VDD

Noduino : 51R is connected to AVCC,AREF and 51R+51R is connected to VCC,

Can you tell me logic behind these resistor?
for example what will be resistor if i want to attack attiny85?

We usually just choose a reasonable size for a shunt resistor and adjust from there - a larger resistance will give better power traces, but may cause the target not to function.