I've just implemented a new feature so that I can find Bat, Crab, Gartley, or Butterfly pattern in the chart. You can find the latest code from https://gist.github.com/masayang/215ca81f6e137857b160

Attached image is AKAM 15min chart. It's amazing the price reversed at $46.66, which is 1.618XA.

Now I need to find how to create a condition from my indicator.

Here is an updated version. Now it displays AB=CD target as well as BAT, Gartley, Crab, or Butterfly target when available.

	Public Overrides function Plot() as System.Single
		' Original: http://forums.worden.com/default.aspx?g=posts&t=42846
		
		'# Period = UserInput.Single = 14
		'# Factor = UserInput.Single = 3
		
		Static ZZ As MyZigZag
		Static XABCD As XABCD
		
		If isFirstBar Then
			ZZ = New MyZigZag(Price, Period, Factor)
			XABCD = New XABCD()
			Plot = Single.NaN
		Else
			ZZ.PrePlot(Price)
			If ZZ.IsExtreme(Price) Then 
				XABCD.AddExtreme(ZZ.GetExtremePrice())
				AddToOutput(ZZ.GetExtremeDate(), ZZ.GetExtremePrice())
			End If
			ZZ.PostPlot(Price, Factor)
		End If
		If isLastBar Then 
			XABCD.AddExtreme(ZZ.GetExtremePrice())
			AddToOutput(ZZ.GetExtremeDate(), ZZ.GetExtremePrice, XABCD.Display())
		End If
		
		Plot = Single.NaN	
		

end function
End Class

Class XABCD
	Private _Extremes(5) As Single
	Private _Output As String
	
	Public Sub New()
		_Extremes(0) = Single.NaN 'D
		_Extremes(1) = Single.NaN 'C
		_Extremes(2) = Single.NaN 'B
		_Extremes(3) = Single.NaN 'A
		_Extremes(4) = Single.NaN 'X
		_Output = ""
	End Sub
	
	Public Sub AddExtreme(Value As Single)
		_Extremes(4) = _Extremes(3)
		_Extremes(3) = _Extremes(2)
		_Extremes(2) = _Extremes(1)
		_Extremes(1) = _Extremes(0)
		_Extremes(0) = Value
	End Sub
	
	Private Function XA() As Single
		Return _Extremes(3) - _Extremes(4)
	End Function
	
	Private Function AB() As Single
		Return _Extremes(3) - _Extremes(2)
	End Function
	
	Private Function BC() As Single
		Return _Extremes(1) - _Extremes(2)
	End Function
	
	Private Function CD() As Single
		Return _Extremes(1) - _Extremes(0)
	End Function
	
	Private Function isCrab() As Boolean
		&#39;AB >= 0.382XA and AB <=0.618XA
		If AB() < 0.352 * XA() Then Return False
		If AB() > 0.648 * XA() Then Return False
		&#39;BC >= 0.382AB and BC <= 0.886AB
		If BC() < 0.352 * AB() Then Return False
		If BC() > 0.916 * AB() Then Return False
		&#39;CD >= 2.618BC and CD <= 3.618CD
		&#39;If CD() < 2.588 * BC() Then Return False
		&#39;If CD() > 3.648 * BC() Then Return False
		Return True
	End Function
	
	Private Function isDeepCrab() As Boolean
		&#39;AB=0.886XA
		If AB() < 0.856 * XA() Then Return False
		If AB() > 0.916 * XA() Then Return False
		&#39;BC >= 0.382AB and BC < 0.886AB
		If BC() < 0.352 * AB() Then Return False
		If BC() > 0.916 * AB() Then Return False
		&#39;CD >= 2.24BC and CD <= 3.618BC
		&#39;If CD() < 2.21 * BC() Then Return False
		&#39;If CD() > 3.648 * BC() Then Return False
		Return True
	End Function
	
	Private Function isButterfly() As Boolean
		&#39;AB=0.786XA
		If AB() < 0.756 * XA() Then Return False
		If AB() > 0.816 * XA() Then Return False
		&#39;BC>=0.382AB and BC<=0.886AB
		If BC() < 0.352 * AB() Then Return False
		If BC() > 0.916 * AB() Then Return False
		&#39;CD>=1.618BC and CD<=2.24BC
		&#39;If CD() < 1.588 * BC() Then Return False
		&#39;If CD() > 2.27 * BC() Then Return False
		Return True
	End Function
	
	Private Function isGartley() As Boolean
		&#39;AB=0.618XA
		If AB() < 0.588 * XA() Then Return False
		If AB() > 0.648 * XA() Then Return False
		&#39;=and(C7>=0.382, C7<=0.886)
		&#39;BC >= 0.382AB and BC <= 0.886AB
		If BC() < 0.352 * AB() Then Return False
		If BC() > 0.916 * AB() Then Return False
		&#39;CD >= 1.13BC and CD <= 1.618BC
		&#39;If CD() < 1.1 * BC() Then Return False
		&#39;If CD() > 0.916 * BC() Then Return False
		Return True
	End Function
	
	Private Function isBAT() As Boolean
		&#39;AB >= 0.382XA AND AB <= 0.5XA
		If AB() < 0.382 * XA() Then Return False
		If AB() > 0.5 * XA() Then Return False
		&#39;BC >= 0.382AB and BC <= 0.886AB
		If BC() < 0.382 * AB() Then Return False
		If BC() > 0.886 * AB() Then Return False
		&#39;=and(C8>=1.618, C8<=2.618)
		&#39;CD >= 1.618BC and CD <= 2.618BC
		&#39;If CD() < 1.618 * BC() Then Return False
		&#39;If CD() > 2.618 * BC() Then Return False
		Return True
	End Function
	
	Private Sub _AddToOutput(Str As String)
		_Output = _Output & Str & System.Environment.NewLine
	End Sub
	
	Private Function BatTarget() As Single
		&#39;A - * 0.886XA
		Return _Extremes(3) - XA() * 0.886
	End Function
	
	Private Function GartleyTarget() As Single
		&#39;A - 0.786XA
		return _Extremes(3)-0.786*XA()
	End Function
	
	Private Function CrabTarget() As Single
		&#39;A - 1.618*XA
		return _Extremes(3) - 1.618*XA()
	End Function
	
	Private Function DeepCrabTarget() As Single
		return CrabTarget()
	End Function
	
	Private Function ButterflyTarget() As Single
		&#39;A - 1.27XA()
		Return _Extremes(3) - 1.27 * XA()
	End Function
	
	Private Function ABCDTarget() As Single
		Return _Extremes(1) - AB()	
	End Function
	
	Public Function Display() As String
		_AddToOutput("AB=CD Target=" & ABCDTarget())
		If isBAT() Then _AddToOutput("BAT Target=" & BatTarget())
		If isGartley() Then _AddToOutput("Gartley Target=" & GartleyTarget())
		If isCrab() Then _AddToOutput("Crab Target=" & CrabTarget())
		If isDeepCrab() Then _AddToOutput("Deep Crab Target=" & DeepCrabTarget())
		If isButterfly() Then _AddToOutput("Butterfly Target=" & ButterflyTarget())
		Return _Output
	End Function
End Class

Class MyZigZaG
	Private _TR As Single
	Private _TermRatio As Single
	Private _ATR As Single
	Private _SumWeight As Single
	Private _Weight As Single
	Private _ExtDate As Date
	Private _Extreme As Single
	Private _Tstop As Single
	Private _State As ZZState
	
	Public Sub New(Price, Period, Factor)
		_TR = Price.High - Price.Low
		_TermRatio = (Period - 1) / Period
		_ATR = _TR
		_SumWeight = _TermRatio + 1
		_Weight = 1 / _SumWeight
		_ExtDate = Price.DateValue
		
		If _StartsFromExtremeLow(Price) Then
			_Extreme = Price.Low
			_Tstop = System.Math.Max(Price.High, _Extreme + Factor * _ATR)
			_State = ZZState.Down
		Else
			_Extreme = Price.High
			_Tstop = System.Math.Min(Price.Low, _Extreme - Factor * _ATR)
			_State = ZZState.Up
		End If
	End Sub
	
	Private Function _StartsFromExtremeLow(Price) As Boolean
		Return  Price.High(-1) - System.Math.Min(Price.Low, Price.Low(-1)) < _
			System.Math.Max(Price.High, Price.High(-1)) - Price.Low(-1)
	End Function
	
	Public Function GetExtremeDate() As Date
		Return _ExtDate
	End Function
	
	Public Function GetExtremePrice() As Single
		Return _Extreme
	End Function
	
	Private Sub _SetDownState()
		_State = ZZState.Down
	End Sub
	
	Private Sub _SetUpState()
		_State = ZZState.Up
	End Sub
		
	Public Sub PrePlot(Price)
		_TR = (Price.High - Price.Low + _
			System.Math.Abs(Price.High - Price.Last(1)) + _
			System.Math.Abs(Price.Last(1) - Price.Low)) / 2
		_ATR = _ATR * (1 - _Weight) + _Weight * _TR
		_SumWeight = _SumWeight * _TermRatio + 1
		_Weight = 1 / _SumWeight
	End Sub
	
	Private Function _IsUp() As Boolean
		Return _State = ZZState.Up
	End Function
	
	Private Function _IsDown() As Boolean
		Return _State = ZZState.Down
	End Function
	
	Private Sub _UpdateDirectionToDown(Price, Factor)
		_SetDownState()
		_Extreme = Price.Low
		_ExtDate = Price.DateValue
		_TStop = System.Math.Max(Price.High, GetExtremePrice() + factor * _ATR)		
	End Sub
	
	Private Sub _UpdateDirectionToUp(Price, Factor)
		_SetUpState()
		_Extreme = Price.High
		_ExtDate = Price.DateValue
		_TStop = System.Math.Min(Price.Low, GetExtremePrice() - factor * _ATR)
	End Sub
	
	Private Sub _UpdateDirection(Price, Factor)
		If _IsUp() And (Price.Low < _TStop) Then
			_UpdateDirectionToDown(Price, Factor)
		ElseIf _IsDown() And (Price.High > _TStop) Then
			_UpdateDirectionToUp(Price, Factor)
		End If
	End Sub

	Private Sub _UpdateExtremeHigh(Price, Factor)
		If Price.High >= GetExtremePrice() Then
			_Extreme = Price.High
			_ExtDate = Price.DateValue
		End If
		_TStop = System.Math.Max(_TStop, GetExtremePrice() - factor * _ATR)
	End Sub
	
	Private Sub _UpdateExtremeLow(Price, Factor)
		If Price.Low <= GetExtremePrice Then
			_Extreme = Price.Low
			_ExtDate = Price.DateValue
		End If
		_TStop = System.Math.Min(_TStop, GetExtremePrice() + Factor * _ATR)
	End Sub
	Private Sub _UpdateExtreme(Price, Factor)
		If _IsUp() Then 
			_UpdateExtremeHigh(Price, Factor)
		Else 
			_UpdateExtremeLow(Price, Factor)
		End If
	End Sub
	
	Public Sub PostPlot(Price, Factor)
		_UpdateDirection(Price, Factor)
		_UpdateExtreme(Price, Factor)
	End Sub
	
	Public Function IsExtreme(Price) As Boolean
		If _state = ZZState.Up And Price.Low < _TStop Then Return True
		If _State = ZZState.Down And Price.High > _TStop Then Return True
		Return False
	End Function
End Class

Enum ZZState
	Up = 1
	Down = 2
End Enum

Sorry folks. I confirmed that code didn't work. 

Hmm. That code works on my environment, SF 5.0.39.17229 on Windows Server 2012.  What kind of error did you get actually?

Oops. Discard previous code as I pasted a wrong one. Here is the working version.

Public partial Class RealCodeIndicator 
	Inherits RealCodeIndicator_base
    Public Overrides function Plot() as System.Single
		' Original: http://forums.worden.com/default.aspx?g=posts&t=42846
		
		'# Period = UserInput.Single = 14
		'# Factor = UserInput.Single = 3
		
		Static ZZ As MyZigZag
		Static ABCD As ABCD
		
		If isFirstBar Then
			ZZ = New MyZigZag(Price, Period, Factor)
			ABCD = New ABCD()
			Plot = Single.NaN
		Else
			ZZ.PrePlot(Price)
			If ZZ.IsExtreme(Price) Then 
				ABCD.AddExtreme(ZZ.GetExtremePrice())
				AddToOutput(ZZ.GetExtremeDate(), ZZ.GetExtremePrice())
			End If
			ZZ.PostPlot(Price, Factor)
		End If
		If isLastBar Then 
			ABCD.AddExtreme(ZZ.GetExtremePrice())
			AddToOutput(ZZ.GetExtremeDate(), ZZ.GetExtremePrice, ABCD.Display())
		End If
		
		Plot = Single.NaN
	End Function
End Class

Class ABCD
	Private _Extremes(4) As Single
	Private _Output As String
	
	Public Sub New()
		_Extremes(0) = Single.NaN
		_Extremes(1) = Single.NaN
		_Extremes(2) = Single.NaN
		_Extremes(3) = Single.NaN
		_Output = ""
	End Sub
	
	Public Sub AddExtreme(Value As Single)
		_Extremes(3) = _Extremes(2)
		_Extremes(2) = _Extremes(1)
		_Extremes(1) = _Extremes(0)
		_Extremes(0) = Value
	End Sub
	
	Private Sub _AddToOutput(Str As String)
		_Output = _Output & Str & System.Environment.NewLine
	End Sub
	
	Private Function _OutputAsC()
		Dim Out As String = "If this is C Then" & System.Environment.NewLine
		Dim AB As Single = _Extremes(1) - _Extremes(2)
		Return Out & " D would be " & AB + _Extremes(0)
	End Function

	Private Function _OutputAsD()
		Dim Out As String = "If this is D Then" & System.Environment.NewLine
		Dim AB As Single = _Extremes(2) - _Extremes(3)
		Return Out & " Target would be " & AB + _Extremes(1)
	End Function
	
	Public Function Display() As String
		_AddToOutput(_OutputAsC())
		_AddToOutput(_OutputAsD())
		Return _Output
	End Function
End Class

Class MyZigZaG
	Private _TR As Single
	Private _TermRatio As Single
	Private _ATR As Single
	Private _SumWeight As Single
	Private _Weight As Single
	Private _ExtDate As Date
	Private _Extreme As Single
	Private _Tstop As Single
	Private _State As ZZState
	
	Public Sub New(Price, Period, Factor)
		_TR = Price.High - Price.Low
		_TermRatio = (Period - 1) / Period
		_ATR = _TR
		_SumWeight = _TermRatio + 1
		_Weight = 1 / _SumWeight
		_ExtDate = Price.DateValue
		
		If _StartsFromExtremeLow(Price) Then
			_Extreme = Price.Low
			_Tstop = System.Math.Max(Price.High, _Extreme + Factor * _ATR)
			_State = ZZState.Down
		Else
			_Extreme = Price.High
			_Tstop = System.Math.Min(Price.Low, _Extreme - Factor * _ATR)
			_State = ZZState.Up
		End If
	End Sub
	
	Private Function _StartsFromExtremeLow(Price) As Boolean
		Return  Price.High(-1) - System.Math.Min(Price.Low, Price.Low(-1))  _TStop) Then
			_UpdateDirectionToUp(Price, Factor)
		End If
	End Sub

	Private Sub _UpdateExtremeHigh(Price, Factor)
		If Price.High >= GetExtremePrice() Then
			_Extreme = Price.High
			_ExtDate = Price.DateValue
		End If
		_TStop = System.Math.Max(_TStop, GetExtremePrice() - factor * _ATR)
	End Sub
	
	Private Sub _UpdateExtremeLow(Price, Factor)
		If Price.Low  _TStop Then Return True
		Return False
	End Function
End Class

Enum ZZState
	Up = 1
	Down = 2
End Enum

Here is an another new member.  I'm new to StockFinder as well as harmonics, but I learned harmonics had great potential for swing trades. I appreciate pthegreat (Peter?) for providing us a nice coding example.

While I was using and reading Peter's code from this thread, I thought I could improve the implementation;

Using ATR to remove *noise* from ZigZag

I sometimes got annoyed by the fact that a small spike/dip of price would trigger flipping AB=CD target. Since I'm a midium term swing trader, I wanted to ignore those small price movement, then I found someone wrote a code that uses ATR  to determin the threshold of ZigZag. See http://forums.worden.com/default.aspx?g=posts&t=42846

Decoupling of model and view (aka "separation of concerns")

As a Python programmer, I would say most of those examples of RealCode are !#$@!#%*$. Many people are stuffing up monolithtic code into Plot() method. I still think Plot() is a good place to write a simple and small indicator, but I disagree to put everything inside Plot() when the indicator is complicated.

So.... I wrote my own version of AB=CD indicator. I would say this is an MVP (Minimum Viable Product). It only provides AB=CD target at this moment. I'll add more features day by day.

Public partial Class RealCodeIndicator 
	Inherits RealCodeIndicator_base
    Public Overrides function Plot() as System.Single
		' Original: http://forums.worden.com/default.aspx?g=posts&t=42846
		
		'# Period = UserInput.Single = 14
		'# Factor = UserInput.Single = 3
		
		Static ZZ As MyZigZag
		Static ABCD As ABCD
		
		If isFirstBar Then
			ZZ = New MyZigZag(Price, Period, Factor)
			ABCD = New ABCD()
			Plot = Single.NaN
		Else
			ZZ.PrePlot(Price)
			If ZZ.IsExtreme(Price) Then 
				ABCD.AddExtreme(ZZ.GetExtremePrice())
				AddToOutput(ZZ.GetExtremeDate(), ZZ.GetExtremePrice())
			End If
			ZZ.PostPlot(Price, Factor)
		End If
		If isLastBar Then AddToOutput(ZZ.GetExtremeDate(), ZZ.GetExtremePrice)
		Plot = Single.NaN

end function
End Class

Class ABCD
	Private _Extremes(4) As Single
	
	Public Sub New()
		_Extremes(0) = Single.NaN
		_Extremes(1) = Single.NaN
		_Extremes(2) = Single.NaN
		_Extremes(3) = Single.NaN
	End Sub
	
	Public Sub AddExtreme(Value As Single)
		_Extremes(3) = _Extremes(2)
		_Extremes(2) = _Extremes(1)
		_Extremes(1) = _Extremes(0)
		_Extremes(0) = Value
	End Sub
End Class

Class MyZigZaG
	Private _TR As Single
	Private _TermRatio As Single
	Private _ATR As Single
	Private _SumWeight As Single
	Private _Weight As Single
	Private _ExtDate As Date
	Private _Extreme As Single
	Private _Tstop As Single
	Private _State As ZZState
	
	Public Sub New(Price, Period, Factor)
		_TR = Price.High - Price.Low
		_TermRatio = (Period - 1) / Period
		_ATR = _TR
		_SumWeight = _TermRatio + 1
		_Weight = 1 / _SumWeight
		_ExtDate = Price.DateValue
		
		If _StartsFromExtremeLow(Price) Then
			_Extreme = Price.Low
			_Tstop = System.Math.Max(Price.High, _Extreme + Factor * _ATR)
			_State = ZZState.Down
		Else
			_Extreme = Price.High
			_Tstop = System.Math.Min(Price.Low, _Extreme - Factor * _ATR)
			_State = ZZState.Up
		End If
	End Sub
	
	Private Function _StartsFromExtremeLow(Price) As Boolean
		Return  Price.High(-1) - System.Math.Min(Price.Low, Price.Low(-1)) < _
			System.Math.Max(Price.High, Price.High(-1)) - Price.Low(-1)
	End Function
	
	Public Function GetExtremeDate() As Date
		Return _ExtDate
	End Function
	
	Public Function GetExtremePrice() As Single
		Return _Extreme
	End Function
	
	Private Sub _SetDownState()
		_State = ZZState.Down
	End Sub
	
	Private Sub _SetUpState()
		_State = ZZState.Up
	End Sub
		
	Public Sub PrePlot(Price)
		_TR = (Price.High - Price.Low + _
			System.Math.Abs(Price.High - Price.Last(1)) + _
			System.Math.Abs(Price.Last(1) - Price.Low)) / 2
		_ATR = _ATR * (1 - _Weight) + _Weight * _TR
		_SumWeight = _SumWeight * _TermRatio + 1
		_Weight = 1 / _SumWeight
	End Sub
	
	Private Function _IsUp() As Boolean
		Return _State = ZZState.Up
	End Function
	
	Private Function _IsDown() As Boolean
		Return _State = ZZState.Down
	End Function
	
	Private Sub _UpdateDirectionToDown(Price, Factor)
		_SetDownState()
		_Extreme = Price.Low
		_ExtDate = Price.DateValue
		_TStop = System.Math.Max(Price.High, GetExtremePrice() + factor * _ATR)		
	End Sub
	
	Private Sub _UpdateDirectionToUp(Price, Factor)
		_SetUpState()
		_Extreme = Price.High
		_ExtDate = Price.DateValue
		_TStop = System.Math.Min(Price.Low, GetExtremePrice() - factor * _ATR)
	End Sub
	
	Private Sub _UpdateDirection(Price, Factor)
		If _IsUp() And (Price.Low < _TStop) Then
			_UpdateDirectionToDown(Price, Factor)
		ElseIf _IsDown() And (Price.High > _TStop) Then
			_UpdateDirectionToUp(Price, Factor)
		End If
	End Sub

	Private Sub _UpdateExtremeHigh(Price, Factor)
		If Price.High >= GetExtremePrice() Then
			_Extreme = Price.High
			_ExtDate = Price.DateValue
		End If
		_TStop = System.Math.Max(_TStop, GetExtremePrice() - factor * _ATR)
	End Sub
	
	Private Sub _UpdateExtremeLow(Price, Factor)
		If Price.Low <= GetExtremePrice Then
			_Extreme = Price.Low
			_ExtDate = Price.DateValue
		End If
		_TStop = System.Math.Min(_TStop, GetExtremePrice() + Factor * _ATR)
	End Sub
	Private Sub _UpdateExtreme(Price, Factor)
		If _IsUp() Then 
			_UpdateExtremeHigh(Price, Factor)
		Else 
			_UpdateExtremeLow(Price, Factor)
		End If
	End Sub
	
	Public Sub PostPlot(Price, Factor)
		_UpdateDirection(Price, Factor)
		_UpdateExtreme(Price, Factor)
	End Sub
	
	Public Function IsExtreme(Price) As Boolean
		If _state = ZZState.Up And Price.Low < _TStop Then Return True
		If _State = ZZState.Down And Price.High > _TStop Then Return True
		Return False
	End Function
End Class

Enum ZZState
	Up = 1
	Down = 2
End Enum