QPolygonF precision?! is it possible?!

[fatecasino]

I have this QPolygonF

selectedPolygon<< QPointF(1.47 ,52.21);
    selectedPolygon<< QPointF(1.50 ,53.12);
    selectedPolygon<< QPointF(1.52 ,54.48);
    selectedPolygon<< QPointF(1.55,55.84);
    selectedPolygon<< QPointF(1.57 ,57.20);
    selectedPolygon<< QPointF(1.60 ,58.57);
  .....................................
    selectedPolygon<< QPointF(1.73 ,66.28);
    selectedPolygon<< QPointF(1.75 ,68.10);
    selectedPolygon<< QPointF(1.78 ,69.92);
    selectedPolygon<< QPointF(1.80,72.19);
    selectedPolygon<< QPointF(1.83 ,74.46);

selectedPolygon<< QPointF(1.47 ,52.21);
    selectedPolygon<< QPointF(1.50 ,53.12);
    selectedPolygon<< QPointF(1.52 ,54.48);
    selectedPolygon<< QPointF(1.55,55.84);
    selectedPolygon<< QPointF(1.57 ,57.20);
    selectedPolygon<< QPointF(1.60 ,58.57);
  .....................................
    selectedPolygon<< QPointF(1.73 ,66.28);
    selectedPolygon<< QPointF(1.75 ,68.10);
    selectedPolygon<< QPointF(1.78 ,69.92);
    selectedPolygon<< QPointF(1.80,72.19);
    selectedPolygon<< QPointF(1.83 ,74.46);

To copy to clipboard, switch view to plain text mode 

and in debug mode when I get back these values:

int N = selectedPolygon.size();
    for (int i = 0; i < N; i++)
    {
        x = selectedPolygon.at(i).x();
        y = selectedPolygon.at(i).y();
........
    }

int N = selectedPolygon.size();
    for (int i = 0; i < N; i++)
    {
        x = selectedPolygon.at(i).x();
        y = selectedPolygon.at(i).y();
........
    }

To copy to clipboard, switch view to plain text mode 

the values comeback as:

(1.47, 52.210000000000001)
(1.5, 53.119999999999997)
(1.52, 54.479999999999997)
(1.55, 55.840000000000003)
(1.5700000000000001, 57.200000000000003)
.........................

(1.47, 52.210000000000001)
(1.5, 53.119999999999997)
(1.52, 54.479999999999997)
(1.55, 55.840000000000003)
(1.5700000000000001, 57.200000000000003)
.........................

To copy to clipboard, switch view to plain text mode 

this change causes huge errors to my calculations!!!!!!
why is this happening? is there a way to avoid it??!