diff --git a/src/configuration.cpp b/src/configuration.cpp
index 6bd3b3d..4386dba 100644
--- a/src/configuration.cpp
+++ b/src/configuration.cpp
@@ -111,7 +111,7 @@ void Configuration::readFile(fs::FS &fs, const char *fileName) {
 bool Configuration::validateConfigFile(String currentBeaconCallsign) {
     if (currentBeaconCallsign.indexOf("NOCALL") != -1) {
         logger.log(logging::LoggerLevel::LOGGER_LEVEL_ERROR, "Config", "Change all your callsigns in 'data/tracker_config.json' and upload it via 'Upload File System image'");
-        show_display("ERROR", "Callsigns = NOCALL!", "---> change it !!!");
+        show_display("ERROR", "Callsigns = NOCALL!", "---> change it !!!", 2000);
         return true;
     } else {
         return false;
diff --git a/src/display.cpp b/src/display.cpp
index f8a4103..be5e7d0 100644
--- a/src/display.cpp
+++ b/src/display.cpp
@@ -145,7 +145,7 @@ void display_toggle(bool toggle) {
     }
 }
 
-void show_display(String header, String line1, String line2, int wait) {
+void show_display(const String& header, const String& line1, const String& line2, int wait) {
     #ifdef HAS_TFT
         cleanTFT();
         tft.setTextColor(TFT_WHITE,TFT_BLACK);
@@ -181,7 +181,7 @@ void show_display(String header, String line1, String line2, int wait) {
     delay(wait);
 }
 
-void show_display(String header, String line1, String line2, String line3, String line4, String line5, int wait) {
+void show_display(const String& header, const String& line1, const String& line2, const String& line3, const String& line4, const String& line5, int wait) {
     #ifdef HAS_TFT
         if (menuDisplay != lastMenuDisplay) {
             lastMenuDisplay = menuDisplay;
@@ -298,14 +298,12 @@ void show_display(String header, String line1, String line2, String line3, Strin
     delay(wait);
 }
 
-void startupScreen(uint8_t index, String version) {
+void startupScreen(uint8_t index, const String& version) {
     String workingFreq = "    LoRa Freq [";
-    if (index == 0) {
-        workingFreq += "Eu]";
-    } else if (index == 1) {
-        workingFreq += "PL]";
-    } else if (index == 2) {
-        workingFreq += "UK]";
+    switch (index) {
+        case 0: workingFreq += "Eu]"; break;
+        case 1: workingFreq += "PL]"; break;
+        case 2: workingFreq += "UK]"; break;
     }
     show_display(" LoRa APRS", "      (TRACKER)", workingFreq, "", "Richonguzman / CA2RXU", "      " + version, 4000);
     #ifdef HAS_TFT
diff --git a/src/display.h b/src/display.h
index 2b63e6a..7482a4d 100644
--- a/src/display.h
+++ b/src/display.h
@@ -5,9 +5,9 @@ void setup_display();
 void display_toggle(bool toggle);
 void cleanTFT();
 
-void show_display(String header, String line1, String line2, int wait = 0);
-void show_display(String header, String line1, String line2, String line3, String line4, String line5, int wait = 0);
+void show_display(const String& header, const String& line1, const String& line2, int wait = 0);
+void show_display(const String& header, const String& line1, const String& line2, const String& line3, const String& line4, const String& line5, int wait = 0);
 
-void startupScreen(uint8_t index, String version);
+void startupScreen(uint8_t index, const String& version);
 
 #endif
\ No newline at end of file
diff --git a/src/gps_utils.cpp b/src/gps_utils.cpp
index e55c2a0..22a109f 100644
--- a/src/gps_utils.cpp
+++ b/src/gps_utils.cpp
@@ -50,11 +50,11 @@ namespace GPS_Utils {
         neo6m_gps.begin(GPS_BAUD, SERIAL_8N1, GPS_TX, GPS_RX);
     }
 
-    void calculateDistanceCourse(String Callsign, double checkpointLatitude, double checkPointLongitude) {
+    void calculateDistanceCourse(const String& callsign, double checkpointLatitude, double checkPointLongitude) {
         double distanceKm = TinyGPSPlus::distanceBetween(gps.location.lat(), gps.location.lng(), checkpointLatitude, checkPointLongitude) / 1000.0;
         double courseTo   = TinyGPSPlus::courseTo(gps.location.lat(), gps.location.lng(), checkpointLatitude, checkPointLongitude);
         STATION_Utils::deleteListenedTrackersbyTime();
-        STATION_Utils::orderListenedTrackersByDistance(Callsign, distanceKm, courseTo);
+        STATION_Utils::orderListenedTrackersByDistance(callsign, distanceKm, courseTo);
     }
 
     void getData() {
diff --git a/src/gps_utils.h b/src/gps_utils.h
index ca97d95..18aaef3 100644
--- a/src/gps_utils.h
+++ b/src/gps_utils.h
@@ -6,7 +6,7 @@
 namespace GPS_Utils {
 
     void setup();
-    void calculateDistanceCourse(String Callsign, double checkpointLatitude, double checkPointLongitude);
+    void calculateDistanceCourse(const String& callsign, double checkpointLatitude, double checkPointLongitude);
     void getData();
     void setDateFromData();
     void calculateDistanceTraveled();