Drasive

You are correct, my class had a pretty big bug in it, thanks for pointing that out. I updated it and it should work fine now.

I extended the class a little further:

using System;

namespace System.Diagnostics {
    
    public class Stopwatch {
        
        private long _ticksAtStart;
        private long _ticksNow;
        
        
        public bool IsRunning { get; private set; }
        
        public TimeSpan ElapsedDuration {
            get {
                return IsRunning ? new TimeSpan(0, 0, 0, 0, (int)((Microsoft.SPOT.Hardware.Utility.GetMachineTime().Ticks - _ticksAtStart) / TimeSpan.TicksPerMillisecond))
                                 : new TimeSpan(0, 0, 0, 0, (int)((_ticksNow - _ticksAtStart) / TimeSpan.TicksPerMillisecond));
            }
        }
        
        
        public void Start() {
            _ticksAtStart = Microsoft.SPOT.Hardware.Utility.GetMachineTime().Ticks;
            IsRunning = true;
        }
        
        public void Stop() {
            if (!IsRunning) {
                throw new InvalidOperationException();
            }
            
            _ticksNow = Microsoft.SPOT.Hardware.Utility.GetMachineTime().Ticks;
            IsRunning = false;
        }
        
        public void Resume() {
            if (IsRunning) {
                throw new InvalidOperationException();
            }
            
            _ticksAtStart = Microsoft.SPOT.Hardware.Utility.GetMachineTime().Ticks - (_ticksNow - _ticksAtStart);
            IsRunning = true;
        }
        
        public void Reset() {
            _ticksAtStart = 0;
            _ticksNow = 0;
            IsRunning = false;
        }
        
    }
    
}