convert double to string?

hi,
i've got this error with this code...?:
Cannot implicitly convert type 'double' to 'string'
if (Convert.ToDouble(Label1.Text) >= Convert.ToDouble(Label55.Text))
Line 147: {
Line 148: Label1.Text = ((Convert.ToDouble(Label1.Text) - Convert.ToDouble("0.5")));
...