diff --git a/OSBindings/Mac/Clock Signal/Wrappers/CSAtari2600.mm b/OSBindings/Mac/Clock Signal/Wrappers/CSAtari2600.mm
index 74cc46b7f..2ded5ede0 100644
--- a/OSBindings/Mac/Clock Signal/Wrappers/CSAtari2600.mm	
+++ b/OSBindings/Mac/Clock Signal/Wrappers/CSAtari2600.mm	
@@ -11,37 +11,36 @@
 #import "Atari2600.hpp"
 #import "CSMachine+Subclassing.h"
 
+@interface CSAtari2600 ()
+- (void)crt:(Outputs::CRT::CRT *)crt didEndBatchOfFrames:(unsigned int)numberOfFrames withUnexpectedVerticalSyncs:(unsigned int)numberOfUnexpectedSyncs;
+@end
+
+struct CRTDelegate: public Outputs::CRT::Delegate {
+	__weak CSAtari2600 *atari2600;
+	void crt_did_end_batch_of_frames(Outputs::CRT::CRT *crt, unsigned int number_of_frames, unsigned int number_of_unexpected_vertical_syncs) {
+		[atari2600 crt:crt didEndBatchOfFrames:number_of_frames withUnexpectedVerticalSyncs:number_of_unexpected_vertical_syncs];
+	}
+};
+
 @implementation CSAtari2600 {
 	Atari2600::Machine _atari2600;
+	CRTDelegate _crtDelegate;
 
 	int _frameCount;
 	int _hitCount;
 	BOOL _didDecideRegion;
 }
 
-/*- (void)crt:(Outputs::CRT *)crt didEndFrame:(CRTFrame *)frame didDetectVSync:(BOOL)didDetectVSync {
+- (void)crt:(Outputs::CRT::CRT *)crt didEndBatchOfFrames:(unsigned int)numberOfFrames withUnexpectedVerticalSyncs:(unsigned int)numberOfUnexpectedSyncs {
 	if(!_didDecideRegion)
 	{
-		_frameCount++;
-		_hitCount += didDetectVSync ? 1 : 0;
-
-		if(_frameCount > 30)
+		_didDecideRegion = YES;
+		if(numberOfUnexpectedSyncs >= numberOfFrames >> 1)
 		{
-			if(_hitCount < _frameCount >> 1)
-			{
-				_atari2600.switch_region();
-				_didDecideRegion = YES;
-			}
-
-			if(_hitCount > (_frameCount * 7) >> 3)
-			{
-				_didDecideRegion = YES;
-			}
+			_atari2600.switch_region();
 		}
 	}
-
-	[super crt:crt didEndFrame:frame didDetectVSync:didDetectVSync];
-}*/
+}
 
 - (void)runForNumberOfCycles:(int)numberOfCycles {
 	@synchronized(self) {
@@ -74,6 +73,8 @@
 - (void)setupOutputWithAspectRatio:(float)aspectRatio {
 	@synchronized(self) {
 		_atari2600.setup_output(aspectRatio);
+		_atari2600.get_crt()->set_delegate(&_crtDelegate);
+		_crtDelegate.atari2600 = self;
 	}
 }
 
diff --git a/Outputs/CRT/CRT.cpp b/Outputs/CRT/CRT.cpp
index 6e6e11c90..290174298 100644
--- a/Outputs/CRT/CRT.cpp
+++ b/Outputs/CRT/CRT.cpp
@@ -66,7 +66,9 @@ CRT::CRT(unsigned int common_output_divisor) :
 	_is_receiving_sync(false),
 	_sync_period(0),
 	_common_output_divisor(common_output_divisor),
-	_is_writing_composite_run(false) {}
+	_is_writing_composite_run(false),
+	_delegate(nullptr),
+	_frames_since_last_delegate_call(0) {}
 
 CRT::CRT(unsigned int cycles_per_line, unsigned int common_output_divisor, unsigned int height_of_display, ColourSpace colour_space, unsigned int colour_cycle_numerator, unsigned int colour_cycle_denominator, unsigned int buffer_depth) : CRT(common_output_divisor)
 {
@@ -209,11 +211,6 @@ void CRT::advance_cycles(unsigned int number_of_cycles, unsigned int source_divi
 			}
 		}
 
-//		if(is_output_segment)
-//		{
-//			_openGL_output_builder->complete_output_run(6);
-//		}
-
 		// if this is horizontal retrace then advance the output line counter and bookend an output run
 		if(_openGL_output_builder->get_output_device() == Television)
 		{
@@ -251,8 +248,15 @@ void CRT::advance_cycles(unsigned int number_of_cycles, unsigned int source_divi
 		// if this is vertical retrace then adcance a field
 		if(next_run_length == time_until_vertical_sync_event && next_vertical_sync_event == Flywheel::SyncEvent::EndRetrace)
 		{
-			// TODO: how to communicate did_detect_vsync? Bring the delegate back?
-//			_delegate->crt_did_end_frame(this, &_current_frame_builder->frame, _did_detect_vsync);
+			if(_delegate)
+			{
+				_frames_since_last_delegate_call++;
+				if(_frames_since_last_delegate_call == 100)
+				{
+					_delegate->crt_did_end_batch_of_frames(this, _frames_since_last_delegate_call, _vertical_flywheel->get_and_reset_number_of_surprises());
+					_frames_since_last_delegate_call = 0;
+				}
+			}
 
 			_openGL_output_builder->increment_field();
 		}
diff --git a/Outputs/CRT/CRT.hpp b/Outputs/CRT/CRT.hpp
index ed4ca7fbd..ed0852666 100644
--- a/Outputs/CRT/CRT.hpp
+++ b/Outputs/CRT/CRT.hpp
@@ -18,6 +18,13 @@
 namespace Outputs {
 namespace CRT {
 
+class CRT;
+
+class Delegate {
+	public:
+		virtual void crt_did_end_batch_of_frames(CRT *crt, unsigned int number_of_frames, unsigned int number_of_unexpected_vertical_syncs) = 0;
+};
+
 class CRT {
 	private:
 		CRT(unsigned int common_output_divisor);
@@ -74,6 +81,10 @@ class CRT {
 		// OpenGL state, kept behind an opaque pointer to avoid inclusion of the GL headers here.
 		std::unique_ptr<OpenGLOutputBuilder> _openGL_output_builder;
 
+		// The delegate;
+		Delegate *_delegate;
+		unsigned int _frames_since_last_delegate_call;
+
 	public:
 		/*!	Constructs the CRT with a specified clock rate, height and colour subcarrier frequency.
 			The requested number of buffers, each with the requested number of bytes per pixel,
@@ -252,6 +263,11 @@ class CRT {
 		}
 
 		Rect get_rect_for_area(int first_line_after_sync, int number_of_lines, int first_cycle_after_sync, int number_of_cycles, float aspect_ratio);
+
+		inline void set_delegate(Delegate *delegate)
+		{
+			_delegate = delegate;
+		}
 };
 
 }
diff --git a/Outputs/CRT/Internals/Flywheel.hpp b/Outputs/CRT/Internals/Flywheel.hpp
index c3a00a3aa..e9bd87ed1 100644
--- a/Outputs/CRT/Internals/Flywheel.hpp
+++ b/Outputs/CRT/Internals/Flywheel.hpp
@@ -36,7 +36,8 @@ struct Flywheel
 		_sync_error_window(standard_period >> 7),
 		_counter(0),
 		_expected_next_sync(standard_period),
-		_counter_before_retrace(standard_period - retrace_time) {}
+		_counter_before_retrace(standard_period - retrace_time),
+		_number_of_surprises(0) {}
 
 	enum SyncEvent {
 		/// Indicates that no synchronisation events will occur in the queried window.