diff --git a/NTPClient.cpp b/NTPClient.cpp
index fffe105..7be57b7 100755
--- a/NTPClient.cpp
+++ b/NTPClient.cpp
@@ -81,6 +81,34 @@ void NTPClient::begin(int port) {
   this->_udpSetup = true;
 }
 
+bool NTPClient::checkResponse() {
+
+  if (this->_udp->parsePacket()) {
+    this->_lastUpdate = millis();
+    this->_lastRequest = 0; // no outstanding request
+    this->_udp->read(this->_packetBuffer, NTP_PACKET_SIZE);
+
+    unsigned long highWord = word(this->_packetBuffer[40], this->_packetBuffer[41]);
+    unsigned long lowWord = word(this->_packetBuffer[42], this->_packetBuffer[43]);
+    // combine the four bytes (two words) into a long integer
+    // this is NTP time (seconds since Jan 1 1900):
+    unsigned long secsSince1900 = highWord << 16 | lowWord;
+
+    this->_currentEpoc = secsSince1900 - SEVENZYYEARS;
+
+    highWord = word(this->_packetBuffer[44], this->_packetBuffer[45]);
+    lowWord = word(this->_packetBuffer[46], this->_packetBuffer[47]);
+    this->_currentFraction = highWord << 16 | lowWord;
+
+    // if the user has set a callback function for when the time is updated, call it
+    if (_updateCallback) { _updateCallback(this); }
+
+    return true;
+  } else {
+    return false;
+  }
+}
+
 bool NTPClient::forceUpdate() {
   #ifdef DEBUG_NTPClient
     Serial.println("Update from NTP Server");
@@ -94,42 +122,60 @@ bool NTPClient::forceUpdate() {
 
   // Wait till data is there or timeout...
   byte timeout = 0;
-  int cb = 0;
+  bool cb = 0;
   do {
     delay ( 10 );
-    cb = this->_udp->parsePacket();
+    cb = this->checkResponse();
     if (timeout > 100) return false; // timeout after 1000 ms
     timeout++;
-  } while (cb == 0);
+  } while (cb == false);
 
-  this->_lastUpdate = millis() - (10 * (timeout + 1)); // Account for delay in reading the time
+  return true;
+}
 
-  this->_udp->read(this->_packetBuffer, NTP_PACKET_SIZE);
+bool NTPClient::update() {
+  bool updated = false;
+  unsigned long now = millis();
 
-  unsigned long highWord = word(this->_packetBuffer[40], this->_packetBuffer[41]);
-  unsigned long lowWord = word(this->_packetBuffer[42], this->_packetBuffer[43]);
-  // combine the four bytes (two words) into a long integer
-  // this is NTP time (seconds since Jan 1 1900):
-  unsigned long secsSince1900 = highWord << 16 | lowWord;
+  if ( ((_lastRequest == 0) && (_lastUpdate == 0))                          // Never requested or updated
+    || ((_lastRequest == 0) && ((now - _lastUpdate) >= _updateInterval))    // Update after _updateInterval
+    || ((_lastRequest != 0) && ((now - _lastRequest) > _retryInterval)) ) { // Update if there was no response to the request
 
-  this->_currentEpoc = secsSince1900 - SEVENZYYEARS;
+    // setup the UDP client if needed
+    if (!this->_udpSetup) {
+      this->begin();
+    }
 
-  return true;  // return true after successful update
-}
+    this->sendNTPPacket();
+  }
 
-bool NTPClient::update() {
-  if ((millis() - this->_lastUpdate >= this->_updateInterval)     // Update after _updateInterval
-    || this->_lastUpdate == 0) {                                // Update if there was no update yet.
-    if (!this->_udpSetup) this->begin();                         // setup the UDP client if needed
-    return this->forceUpdate();
+  if (_lastRequest) {
+    updated = checkResponse();
   }
-  return false;   // return false if update does not occur
+
+  return updated;
+}
+
+bool NTPClient::updated() {
+  return (_currentEpoc != 0);
 }
 
 unsigned long NTPClient::getEpochTime() const {
   return this->_timeOffset + // User offset
          this->_currentEpoc + // Epoc returned by the NTP server
-         ((millis() - this->_lastUpdate) / 1000); // Time since last update
+         ((millis() - this->_lastUpdate + (_currentFraction / FRACTIONSPERMILLI)) / 1000); // Time since last update
+}
+
+unsigned long long NTPClient::getEpochMillis() {
+  unsigned long long epoch;
+
+  epoch = this->_timeOffset;                     // user offset
+  epoch += _currentEpoc;                         // last time returned via server
+  epoch *= 1000;                                 // convert to millis
+  epoch += _currentFraction / FRACTIONSPERMILLI; // add the fraction from the server
+  epoch += millis() - this->_lastUpdate;         // add the millis that have passed since the last update
+
+  return epoch;
 }
 
 int NTPClient::getDay() const {
@@ -173,6 +219,14 @@ void NTPClient::setUpdateInterval(unsigned long updateInterval) {
   this->_updateInterval = updateInterval;
 }
 
+void NTPClient::setRetryInterval(int retryInterval) {
+  _retryInterval = retryInterval;
+}
+
+void NTPClient::setUpdateCallback(NTPUpdateCallbackFunction f) {
+  _updateCallback = f;
+}
+
 void NTPClient::setPoolServerName(const char* poolServerName) {
     this->_poolServerName = poolServerName;
 }
@@ -201,4 +255,7 @@ void NTPClient::sendNTPPacket() {
   }
   this->_udp->write(this->_packetBuffer, NTP_PACKET_SIZE);
   this->_udp->endPacket();
+
+  this->_lastRequest = millis();
+
 }
diff --git a/NTPClient.h b/NTPClient.h
index 20ec43b..df8c626 100755
--- a/NTPClient.h
+++ b/NTPClient.h
@@ -5,9 +5,14 @@
 #include <Udp.h>
 
 #define SEVENZYYEARS 2208988800UL
+#define FRACTIONSPERMILLI (4294967UL)
 #define NTP_PACKET_SIZE 48
 #define NTP_DEFAULT_LOCAL_PORT 1337
 
+class NTPClient;
+
+typedef void (*NTPUpdateCallbackFunction)(NTPClient* c);
+
 class NTPClient {
   private:
     UDP*          _udp;
@@ -18,14 +23,20 @@ class NTPClient {
     int           _port           = NTP_DEFAULT_LOCAL_PORT;
     long          _timeOffset     = 0;
 
+    unsigned int  _retryInterval  = 1000;   // In ms
     unsigned long _updateInterval = 60000;  // In ms
 
     unsigned long _currentEpoc    = 0;      // In s
+    unsigned long _currentFraction = 0;     // In 1/(2^32) s
     unsigned long _lastUpdate     = 0;      // In ms
+    unsigned long _lastRequest    = 0;      // IN ms
 
     byte          _packetBuffer[NTP_PACKET_SIZE];
 
+    NTPUpdateCallbackFunction _updateCallback = NULL;
+
     void          sendNTPPacket();
+    bool          checkResponse();
 
   public:
     NTPClient(UDP& udp);
@@ -63,8 +74,20 @@ class NTPClient {
     bool update();
 
     /**
-     * This will force the update from the NTP Server.
+     * Has the time ever been sucessfully updated
      *
+     */
+    bool updated();
+
+    /**
+     * Register a callback function for when the time gets updated
+     *
+     */
+    void setUpdateCallback(NTPUpdateCallbackFunction f);
+
+    /**
+     * This will force the update from the NTP Server.
+     * This can block for a full second
      * @return true on success, false on failure
      */
     bool forceUpdate();
@@ -85,6 +108,11 @@ class NTPClient {
      */
     void setUpdateInterval(unsigned long updateInterval);
 
+    /**
+     * Set the retry interval to another frequency in ms
+     */
+    void setRetryInterval(int retryInterval);
+
     /**
      * @return time formatted like `hh:mm:ss`
      */
@@ -95,6 +123,11 @@ class NTPClient {
      */
     unsigned long getEpochTime() const;
 
+    /**
+     * @return time in milliseconds since Jan. 1, 1970
+     */
+    unsigned long long getEpochMillis();
+
     /**
      * Stops the underlying UDP client
      */