diff --git a/slsDetectorSoftware/slsDetector/slsDetectorUsers.h b/slsDetectorSoftware/slsDetector/slsDetectorUsers.h
index bda5567e2..0b5948083 100644
--- a/slsDetectorSoftware/slsDetector/slsDetectorUsers.h
+++ b/slsDetectorSoftware/slsDetector/slsDetectorUsers.h
@@ -346,7 +346,7 @@ class slsDetectorUsers
      \param userCallback function for plotting/analyzing the data
   */
 
-  virtual void registerDataCallback(int( *userCallback)(detectorData*))=0;
+  virtual void registerDataCallback(int( *userCallback)(detectorData*, void*), void *pArg)=0;
   
   /**
      @short register calbback for reading detector position
diff --git a/slsDetectorSoftware/slsDetectorAnalysis/postProcessing.cpp b/slsDetectorSoftware/slsDetectorAnalysis/postProcessing.cpp
index 7e3688efa..9bb7e9954 100644
--- a/slsDetectorSoftware/slsDetectorAnalysis/postProcessing.cpp
+++ b/slsDetectorSoftware/slsDetectorAnalysis/postProcessing.cpp
@@ -10,7 +10,8 @@ postProcessing::postProcessing(){
   pthread_mutex_init(&mg, NULL);  
   //cout << "reg callback "<< endl;
   dataReady = 0;
-  registerDataCallback(&defaultDataReadyFunc);
+  pCallbackArg = 0; 
+  registerDataCallback(&defaultDataReadyFunc,  NULL);
   //cout << "done "<< endl;
 }
 
@@ -301,7 +302,7 @@ void postProcessing::doProcessing(float *lfdata, int delflag, string fname) {
 
 	  if (dataReady) {
 
-	    dataReady(thisData);
+	    dataReady(thisData, pCallbackArg);
 	    delete thisData;
 	  }
 
@@ -338,7 +339,7 @@ void postProcessing::doProcessing(float *lfdata, int delflag, string fname) {
 
 
 	if (dataReady) {
-	  dataReady(thisData);
+	  dataReady(thisData, pCallbackArg);
 	  delete thisData;
 	}
 // 	pthread_mutex_lock(&mg);
diff --git a/slsDetectorSoftware/slsDetectorAnalysis/postProcessing.h b/slsDetectorSoftware/slsDetectorAnalysis/postProcessing.h
index 1905b5cc4..f94097450 100644
--- a/slsDetectorSoftware/slsDetectorAnalysis/postProcessing.h
+++ b/slsDetectorSoftware/slsDetectorAnalysis/postProcessing.h
@@ -241,7 +241,7 @@ s
 
 
 
-  void registerDataCallback(int( *userCallback)(detectorData*)) {dataReady = userCallback;};
+  void registerDataCallback(int( *userCallback)(detectorData*, void*),  void *pArg) {dataReady = userCallback; pCallbackArg = pArg;};
   
 
 
@@ -363,8 +363,8 @@ s
 /*   virtual int getTotalNumberOfChannels()=0; */
 
   
-  int (*dataReady)(detectorData*); 
-
+  int (*dataReady)(detectorData*,void*); 
+  void *pCallbackArg; 
 
 };
 
diff --git a/slsDetectorSoftware/usersFunctions/usersFunctions.cpp b/slsDetectorSoftware/usersFunctions/usersFunctions.cpp
index bbdd1509b..1548a733b 100644
--- a/slsDetectorSoftware/usersFunctions/usersFunctions.cpp
+++ b/slsDetectorSoftware/usersFunctions/usersFunctions.cpp
@@ -323,7 +323,7 @@ int defaultDisconnectChannels() {
 
 
 
-int defaultDataReadyFunc(detectorData* d) {
+int defaultDataReadyFunc(detectorData* d,  void* p) {
 #ifdef VERBOSE
   printf("UUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUU Data received \n");
 #endif
diff --git a/slsDetectorSoftware/usersFunctions/usersFunctions.h b/slsDetectorSoftware/usersFunctions/usersFunctions.h
index 24e89e051..e522f5ba5 100644
--- a/slsDetectorSoftware/usersFunctions/usersFunctions.h
+++ b/slsDetectorSoftware/usersFunctions/usersFunctions.h
@@ -37,7 +37,7 @@ extern "C" {
   int defaultDisconnectChannels();
   float defaultGetI0(int t);
   
-  int defaultDataReadyFunc(detectorData* d);
+  int defaultDataReadyFunc(detectorData* d,  void* p);