/// <summary>
        /// Remove an event handler.
        /// </summary>
        /// <param name="clock">Customer of event.</param>
        public void Remove(ContraClock clock)
        {
            clock.ClockWorking -= MessageHandler;

            Console.WriteLine($"{GetType()} unregistered.");
        }
        /// <summary>
        /// Add an event handler.
        /// </summary>
        /// <param name="clock">Customer of event.</param>
        public void Add(ContraClock clock)
        {
            clock.ClockWorking += MessageHandler;

            Console.WriteLine($"{GetType()} registered.");
        }