namespace

using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;
using System.IO; // ***********

namespace P_Angle.Units  // *************
{
  public class P_Angle
  {
    public const double Phi = 3.14159265;
  }
}

namespace P_Angle
{
 public class WinForm : System.Windows.Forms.Form
 {

...