Floating point errors with the same input

Question

It's a bit strange. I get different outputs for the same input for the same code at different times.

this is a very simple calculation, just getting a radian for a given angle in degrees, in a class that processes material like a compass. it started as follows:

public double Radians  
{  
    get   
    {  
        return this.heading_degrees * Math.PI / 180;  
    }  
    set  
    {  
       this.heading_degrees = value * 180 / Math.PI;  
       normalize();  
    }  
}  

(heading_degrees is a member variable in Compass class)
looks fine?
except that I got different results when I “received” a radian for a given angle.
so I went deeper and changed the code, now "get" looks like this:

get  
{  
    //double hd = heading_degrees;  
    double hd = 180.0;  
    //double pi = Math.PI;  
    double pi180 = 0.01745329251; //pi / 180;  
    double result = hd * pi180;  
    //double result = 3.14159265359;  
    return result;  
    //return heading_degrees * Math.PI / 180;  
}  

, , .
= 3,14159265359; 3.14159265359 ,
= hd * pi180; . , 180.0, , . , :
result = 3.1415926518
:
result = 3.1415927410125732

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:

get{ 
double result = 180.0d * 0.01745329251d;
return result;
}

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:

get{
double hd = 180.0d;
double result = hd * 0.01745329251d;
return result;
}

.

:

get{
double hd = 180.0d;
double result = (float)(hd * 0.01745329251d);
return result;
}  

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Answer 1

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