I've been going through a java tutorial, and ran across some strangeness in this small example...

 class SqrRoot {
    public static void main(String args[]) {
        double num,sroot,rerr,resquare;
        
        for(num = 1.0; num < 100.0; num++) {
            sroot = Math.sqrt(num);
            System.out.println("Square root of " + num + " is " + sroot);
            
            // compute rounding error
            resquare = (sroot * sroot);
            rerr = num - resquare;
            System.out.println("Rounding error: num + " - " + resquare + " = " + rerr);
            System.out.println();
        }
    }
}

Square root of 1.0 is 1.0
1.0 - 1.0 = 0.0

Square root of 2.0 is 1.4142135623730951
2.0 - 2.0000000000000004 = -4.440892098500626E-16

Square root of 3.0 is 1.7320508075688772
3.0 - 2.9999999999999996 = 4.440892098500626E-16

....