Stretch sensor, ohm meter wrong readings....

Hello guys.

I have a problem. Well I made my self a stretch sensor with conductive fiber. But when it get stretched ( resistence incrase ) I got reading like resistence decrease. Anyone could help me with that ?

My conductive fiber got aroud 620k ohm to 650k ohm when is stretch ( recording to Ohm meter ). I am using "known" resistor of 600k ohm.

code :

int analogPin= 5;
int raw= 0;
int Vin= 5;
float Vout= 0;
float R1= 600000;
float R2= 0;
float buffer= 0;

void setup()
{
Serial.begin(9600);
}

void loop()
{
raw= analogRead(analogPin);
if(raw) 
{
buffer= raw * Vin;
Vout= (buffer)/1024.0;
buffer= (Vin/Vout) -1;
R2= R1 * buffer;
Serial.print("R2: ");
Serial.println(R2);
delay(100);
}
}

As attachment I add screenshot of readings. When fiber is stretch reading numbers are lower then when its not.
EDIT : Imgur: The magic of the Internet <- here is picture of readings.

My conductive fiber got aroud 620k ohm to 650k ohm when is stretch

What is it when not stretch?
How are your resistors connected?

Yes how is your resistor divider arranged - are you calculating the right equation for that setup?