[buffalobillpatrick]

Thanks A/C

float degF=-40.3085122205+(1.81496452942*psi)+(-0.0101201804003*psi^2)+(3.05234258195e-005*psi^3)+(-3.37963005786e-008*psi^4);

Nope, don't compile:

sketch_subcool_3.ino: In function 'float calc_R290_Saturated_Temp(float)':
sketch_subcool_3:214: error: invalid operands of types 'double' and 'int' to binary 'operator^'
sketch_subcool_3:215: error: invalid operands of types 'double' and 'int' to binary 'operator^'
sketch_subcool_3:215: error: invalid operands of types 'double' and 'int' to binary 'operator^'

float calc_R290_Saturated_Temp(float psi)
{ 

double a = -4.03085122205E+001;
double b = 1.81496452942E+000;
double c = -1.01201804003E-002;
double d = 3.05234258195E-005;
double e = -3.37963005786E-008;

 return (a + (b * psi) + (c * psi*psi) + (d * psi*psi*psi)
           + (e * psi*psi*psi*psi));
       
}  // end calc_R290_Saturated_Temp

BTW, Arduino don't do double floats, it just pretends to, when double is specified in source code the compiler handles them same as single precision float, by actually doing integer add operations..

The above code generates exactly same object code as when data type float is used.