This is meant to go on the FiberCircuit table's OnCreate event. If you put it on the OnUpdate it will go off every time connection manager does anything to a connection with circuits on it and it will bog down the entire process. Also it will throw the recalc button in arcmap out of synch if you have it applied to OnUpdate. It won't corrupt any data but the user experience will be odd and greatly slowed down.

'Declaration
 
<ComVisibleAttribute(True)>
<ClassInterfaceAttribute(ClassInterfaceType.None)>
<GuidAttribute("F6960643-2284-4bbe-A3E8-C04392293B8F")>
<ProgIdAttribute("mmFramework.CircuitCalculatedLengthAU")>
<ComponentCategoryAttribute(ComCategory.SpecialAutoUpdateStrategy)>
Public Class CircuitCalculatedLength 
   Implements Miner.Interop.IMMSpecialAUStrategyEx 

'Usage
 
Dim instance As CircuitCalculatedLength

[ComVisible(true)]
[ClassInterface(ClassInterfaceType.None)]
[Guid("F6960643-2284-4bbe-A3E8-C04392293B8F")]
[ProgId("mmFramework.CircuitCalculatedLengthAU")]
[ComponentCategory(ComCategory.SpecialAutoUpdateStrategy)]
public class CircuitCalculatedLength : Miner.Interop.IMMSpecialAUStrategyEx