Custom datatyper i C#

Hej,

Jeg vil gerne oprette mine egne datatyper i c#.
Jvf. nedenstående link skulle det være nemt nok.

http://vbcity.com/blogs/jatkinson/archive/2010/01/12/create-custom-types-and-initialize-them-without-the-new-keyword-c-vb-net.aspx

Men det virker ikke. Jeg får følgende fejl:

A field initializer cannot reference the non-static field, method, or property 'WindowsFormsApplication1.minklasse.anotherAngle'   

Hvad gør jeg galt ?

Mvh Ole

Her er min kode:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace WindowsFormsApplication1
{
    struct Angle
    {
        // Private constructor called by [implicit operator Angle(...)]
        private Angle(double value)
        {
            // Limiting an angle to the values between -360 and 360 degrees.
            if (value < 360 && value > -360)
            {
                this._angle = value;
            }
            else
            {
                throw new ArgumentOutOfRangeException("value", "variable value must be between -360 and 360 degrees.");
            }
        }

        // Holds an internal value of the angle.
        private double _angle;

        // Here we can initialize a new "Angle" without a constructor.
        public static implicit operator Angle(double value)
        {
            return new Angle(value);
        }

        // Define the "+" behavior.
        public static Angle operator +(Angle a1, Angle a2)
        {
            double temp = a1._angle + a2._angle;
            // Check to see if the addition of two angles is too large
            // to fit in out Angle data type.
            if (temp < 360 && temp > -360)
            {
                return new Angle(temp);
            }
            else
            {
                throw new ArithmeticException();
            }
        }

        // Define "-" behavior.
        public static Angle operator -(Angle a1, Angle a2)
        {
            return new Angle(a1._angle - a2._angle);
        }

        // Type conversions

        // Angle myAngle = 123.45;
        // double d = myAngle;
        public static implicit operator double(Angle value)
        {
            return value._angle;
        }

        // Angle myAngle = 123.45;
        // float f = (float)myAngle;
        public static explicit operator float(Angle value)
        {
            return (float)value._angle;
        }

        // Angle myAngle = 123.45;
        // int i = (int)myAngle;
        public static explicit operator int(Angle value)
        {
            return (int)value._angle;
        }

        public override string ToString()
        {
            return _angle.ToString();
        }
    }

    class minklasse
    {
        // Assignment - virker
        Angle myAngle = 1.23;
        Angle anotherAngle = 90.00;

       
        // Math operations - ingen af disse virker...
        Angle addedAngle = myAngle + anotherAngle;
        Angle KopiAngle = myAngle;
        Angle subtractAngle = myAngle - anotherAngle;
    }
}