Copy text box(numeric double) value to txt file.

Question

I am trying to copy the double value from text box to file but values are written multiple times, Meaning if I write 1.5 in text box I get 1 ,1. , 1.5 in text file

private void textBox1_TextChanged(object sender, EventArgs e)
{
StreamWriter sw = new StreamWriter(@"C:\Delta Sigma\Log.txt",true);
sw.WriteLine("Critical Delta Sigma:", textBox1.Text);

sw.Close();


}