diff --git a/extra_script.py b/extra_script.py
index 8d58014..89efc93 100644
--- a/extra_script.py
+++ b/extra_script.py
@@ -7,6 +7,8 @@ import inspect
 import json
 from datetime import datetime
 Import("env")
+#print(env.Dump())
+OWN_FILE="extra_script.py"
 GEN_DIR='generated'
 CFG_FILE='web/config.json'
 XDR_FILE='web/xdrconfig.json'
@@ -43,6 +45,11 @@ def isCurrent(infile,outfile):
         otime=os.path.getmtime(outfile)
         itime=os.path.getmtime(infile)
         if (otime >= itime):
+            own=os.path.join(basePath(),OWN_FILE)
+            if os.path.exists(own):
+                owntime=os.path.getmtime(own)
+                if owntime > otime:
+                    return False
             print("%s is newer then %s, no need to recreate"%(outfile,infile))
             return True
     return False        
diff --git a/lib/nmea2kto0183/N2kDataToNMEA0183.cpp b/lib/nmea2kto0183/N2kDataToNMEA0183.cpp
index b5bddf8..99c2615 100644
--- a/lib/nmea2kto0183/N2kDataToNMEA0183.cpp
+++ b/lib/nmea2kto0183/N2kDataToNMEA0183.cpp
@@ -72,13 +72,7 @@ private:
 
     String buildXdrEntry(GwXDRFoundMapping &mapping,double value){
         char buffer[40];
-        String name=mapping.definition->xdrName;
-        if (mapping.definition->instanceMode == GwXDRMappingDef::IS_AUTO ||
-            mapping.definition->instanceMode == GwXDRMappingDef::IS_SINGLE
-        ){
-            name+="#";
-            name+=String(mapping.instanceId);
-        }
+        String name=mapping.getTransducerName();
         if (mapping.type->tonmea){
             value=(* (mapping.type->tonmea))(value);
         }
diff --git a/lib/xdrmappings/GwXDRMappings.cpp b/lib/xdrmappings/GwXDRMappings.cpp
index b7f88e7..a0a70bb 100644
--- a/lib/xdrmappings/GwXDRMappings.cpp
+++ b/lib/xdrmappings/GwXDRMappings.cpp
@@ -1,5 +1,6 @@
 #include "GwXDRMappings.h"
 #include "N2kMessages.h"
+
 double PtoBar(double v)
 {
     if (N2kIsNA(v))
@@ -189,6 +190,16 @@ GwXDRMappingDef *GwXDRMappingDef::fromString(String s)
     }
     return rt;
 }
+String GwXDRMappingDef::getTransducerName(int instance)
+{
+    String name = xdrName;
+    if (instanceMode == GwXDRMappingDef::IS_AUTO)
+    {
+        name += "#";
+        name += String(instance);
+    }
+    return name;
+}
 
 GwXDRMappings::GwXDRMappings(GwLog *logger, GwConfigHandler *config)
 {
@@ -373,6 +384,20 @@ bool GwXDRMappings::addUnknown(GwXDRCategory category,int selector,int field,int
     uk=(uk<<7) + (field & 0x7f);
     if (instance < 0 || instance > 255) instance=256; //unknown
     uk=(uk << 9) + (instance & 0x1ff);
-    unknown.push_back(uk);
+    unknown.insert(uk);
     return true;
+}
+
+char * GwXDRMappings::getUnMapped(){
+    const int ESIZE=13;
+    int sz=(unknown.size()+1)*ESIZE;
+    char *rt=new char[sz];
+    *rt=0;
+    char *ptr=rt;
+    for (auto it=unknown.begin();it!=unknown.end();it++){
+        snprintf(ptr,ESIZE-1,"%lu,",*it);
+        *(ptr+ESIZE-1)=0;
+        while (*ptr != 0) ptr++;
+    }
+    return rt;
 }
\ No newline at end of file
diff --git a/lib/xdrmappings/GwXDRMappings.h b/lib/xdrmappings/GwXDRMappings.h
index 66328c0..3c7e7f0 100644
--- a/lib/xdrmappings/GwXDRMappings.h
+++ b/lib/xdrmappings/GwXDRMappings.h
@@ -5,6 +5,7 @@
 #include <WString.h>
 #include <vector>
 #include <map>
+#include <unordered_set>
 //enum must match the defines in xdrconfig.json
 typedef enum {
     XDRTEMP=0,
@@ -124,6 +125,7 @@ class GwXDRMappingDef{
         rt += xdrUnit;
         return rt;
     }
+    String getTransducerName(int instance);
     private:
     static bool handleToken(String tok,int index,GwXDRMappingDef *def);
 };
@@ -157,6 +159,9 @@ class GwXDRFoundMapping{
             empty=false;
         }
         GwXDRFoundMapping(){}
+        String getTransducerName(){
+            return definition->getTransducerName(instanceId);
+        }
 };
 
 class GwXDRMappings{
@@ -165,7 +170,7 @@ class GwXDRMappings{
      GwConfigHandler *config;
      GwXDRMapping::N138Map n183Map;
      GwXDRMapping::N2KMap n2kMap;
-     std::vector<unsigned long> unknown;
+     std::unordered_set<unsigned long> unknown;
      GwXDRFoundMapping selectMapping(GwXDRMapping::MappingList *list,int instance,const char * key);
      bool addUnknown(GwXDRCategory category,int selector,int field=0,int instance=-1);
     public:
@@ -175,6 +180,8 @@ class GwXDRMappings{
         //the returned mapping will exactly contain one mapping def
         GwXDRFoundMapping getMapping(String xName,String xType,String xUnit);
         GwXDRFoundMapping getMapping(GwXDRCategory category,int selector,int field=0,int instance=-1);
+        //returns a newly created buffer - user must destroy!
+        char * getUnMapped();
 
 };