diff --git a/packetmag.cpp b/packetmag.cpp
index 241c864..262346f 100644
--- a/packetmag.cpp
+++ b/packetmag.cpp
@@ -26,7 +26,7 @@ PacketMag::PacketMag(uint8_t mag, std::list<TTXPageStream>* pageSet, ttx::Config
     _cycleDuration(-1)
 {
     //ctor
-    _lastCycle = {0,0};
+    _lastCycleTimestamp = {0,0};
     
     for (int i=0;i<MAXPACKET29TYPES;i++)
     {
@@ -160,12 +160,12 @@ Packet* PacketMag::GetPacket(Packet* p)
                     // get master clock singleton
                     MasterClock *mc = mc->Instance();
                     MasterClock::timeStruct t = mc->GetMasterClock();
-                    if (_lastCycle.seconds){ // wait for real timestamps
-                        int diffSeconds = difftime(t.seconds, _lastCycle.seconds); // truncates double to int
-                        _cycleDuration = ((diffSeconds * 50) - _lastCycle.fields) + t.fields;
+                    if (_lastCycleTimestamp.seconds){ // wait for real timestamps
+                        int diffSeconds = difftime(t.seconds, _lastCycleTimestamp.seconds); // truncates double to int
+                        _cycleDuration = ((diffSeconds * 50) - _lastCycleTimestamp.fields) + t.fields;
                         _debug->SetMagCycleDuration(_magNumber, _cycleDuration);
                     }
-                    _lastCycle = t; // update timestamp
+                    _lastCycleTimestamp = t; // update timestamp
                     
                     // couldn't get a page to send so sent a time filling header
                     p->Header(_magNumber,0xFF,0x0000,0x8010,_headerTemplate);
@@ -435,6 +435,8 @@ bool PacketMag::IsReady(bool force)
         ClearEvent(EVENT_FIELD);
         if (_waitingForField > 0)
         {
+            // _waitingForField is set to 2 when the last packet was a header but field event is not yet cleared
+            // on the next IsReady we clear the event and decrement it ready to wait for the next field event.
             _waitingForField--;
         }
     }
diff --git a/packetmag.h b/packetmag.h
index 90ea100..d4cc2e2 100644
--- a/packetmag.h
+++ b/packetmag.h
@@ -51,6 +51,7 @@ namespace vbit
             bool GetCustomHeaderFlag() { return _hasCustomHeader; };
             void DeleteCustomHeader();
             
+            void InvalidateCycleTimestamp() { _lastCycleTimestamp = {0,0}; }; // reset cycle duration calculation
             int GetCycleDuration() { return _cycleDuration; };
 
         protected:
@@ -92,7 +93,7 @@ namespace vbit
             bool _specialPagesFlipFlop; // toggle to alternate between special pages and normal pages
             int _waitingForField;
             
-            MasterClock::timeStruct _lastCycle;
+            MasterClock::timeStruct _lastCycleTimestamp;
             int _cycleDuration; // magazine cycle time in fields
     };
 }
diff --git a/service.cpp b/service.cpp
index a41c858..4b0c6a9 100644
--- a/service.cpp
+++ b/service.cpp
@@ -12,11 +12,11 @@ Service::Service(Configure *configure, vbit::Debug *debug, PageList *pageList, P
     _packetServer(packetServer),
     _fieldCounter(49) // roll over immediately
 {
-    vbit::PacketMag **magList=_pageList->GetMagazines();
+    _magList=_pageList->GetMagazines();
     // Register all the packet sources
     for (uint8_t mag=0;mag<8;mag++)
     {
-        vbit::PacketMag* m=magList[mag];
+        vbit::PacketMag* m=_magList[mag];
         m->SetPriority(_configure->GetMagazinePriority(mag)); // set the mags to the desired priorities
         _register(m); // use the PacketMags created in pageList rather than duplicating them
     }
@@ -190,6 +190,9 @@ void Service::_updateEvents()
                 masterClock.seconds = now;
                 
                 _debug->Log(Debug::LogLevels::logWARN,"[Service::_updateEvents] Resynchronising master clock");
+                
+                for (int i=0;i<8;i++)
+                    _magList[i]->InvalidateCycleTimestamp(); // reset magazine cycle duration calculations
             }
             
             if (masterClock.seconds%15==0) // TODO: how often do we want to trigger sending special packets?
diff --git a/service.h b/service.h
index 748e21f..baa3d47 100644
--- a/service.h
+++ b/service.h
@@ -57,6 +57,7 @@ namespace ttx
             Configure* _configure; /// Member reference to the configuration settings
             vbit::Debug* _debug;
             PageList* _pageList; /// Member reference to the pages list
+            vbit::PacketMag** _magList;
             PacketServer* _packetServer;
 
             // Member variables for event management