Found it, but tmd3 just beat me to it :-)

I rewrote your code to use an array for the coefficients and input using mV which gives the expected result:

void setup()

{

Serial.begin(9600);

// put your setup code here, to run once:

float mv_sns = 12; // input voltage

// polynomial coefficients:

float poly[9] = {

213.150712,

285.10504,

-52.742887,

9.9160804,

-1.2965303,

0.11195870,

-0.0060625199,

0.00018661696,

-0.0000024878585,

};

// float temp = (c0 + c1 + (c2*c2)+ (c3*c3*c3)+(c4*c4*c4*c4)+(c5*c5*c5*c5*c5)+(c6*c6*c6*c6*c6*c6)+(c7*c7*c7*c7*c7*c7*c7)+(c8*c8*c8*c8*c8*c8*c8*c8));

//float temp2 = ( c0 + (c1*mv_sns) + pow(c2*mv_sns,2) + pow(c3*mv_sns,3) + pow(c4*mv_sns,4) + pow(c5*mv_sns,5) + pow(c6*mv_sns,6) + pow(c7*mv_sns,7) + pow(c8*mv_sns,8));

float temp = 0;

float mult = 1;

for(int i = 0;i < 9;i++) {

temp += mult*poly[i];

mult *= mv_sns;

}

Serial.println(temp,6);

}

void loop() {

// put your main code here, to run repeatedly:

}

Pete