diff --git a/src/main.cpp b/src/main.cpp
index e1909d3..95cfcae 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -14,7 +14,10 @@
 #include "afsk_sinus.hpp"
 
 
+#ifndef SEND_INVALID
 #define SEND_INVALID 0
+#endif
+
 #define DESTINATION "WIDE1 \x01"
 #define TXDELAY 32
 #define FRAME_REPEAT 3
@@ -198,6 +201,7 @@ struct __attribute__((packed)) EepromConfig {
   uint16_t interval;
   uint8_t commentLen;
   uint8_t comment[32];
+  uint8_t positionAmbiguity;
 };
 
 struct EepromConfig config;
@@ -227,6 +231,7 @@ uint32_t lastPressed = 0;
 bool off = true;
 bool editingConfig = false;
 bool editingComment = false;
+bool editingAmbiguity = false;
 uint8_t configEditState = 0;
 uint8_t commentEditState = 0;
 
@@ -254,13 +259,14 @@ uint8_t mirrorByte(uint8_t byt) {
 
 
 void createDefaultConfig() {
-  config.flag = 1;
+  config.flag = 2;
   memset(&config.srcCallsign, ' ', 6);
   config.srcSsid = 0;
   config.marker = 'b';
   config.interval = 300;
   config.commentLen = 0;
   memset(&config.comment, ' ', 32);
+  config.positionAmbiguity = 4;
 }
 
 void writeEepromConfig() {
@@ -503,10 +509,33 @@ void editComment() {
       }
     }
     lcd.print((char) config.comment[commentEditState]);
-      lcd.setCursor(commentEditState%16, commentEditState/16);
+    lcd.setCursor(commentEditState%16, commentEditState/16);
   }
 };
 
+void editAmbiguity() {
+  if (abcPressed) {
+    abcPressed = false;
+    config.positionAmbiguity = (config.positionAmbiguity + 1) % 5;
+  }
+  if (setPressed) {
+    setPressed = false;
+    writeEepromConfig();
+    editingAmbiguity = false;
+    return;
+  }
+  lcd.setCursor(0, 0);
+  lcd.print("Pos. Ambiguity");
+  lcd.setCursor(0, 1);
+  lcd.print(" 47\xdf ");
+  lcd.print(config.positionAmbiguity > 0 ? '1' : '_');
+  lcd.print(config.positionAmbiguity > 1 ? '2' : '_');
+  lcd.print('.');
+  lcd.print(config.positionAmbiguity > 2 ? '3' : '_');
+  lcd.print(config.positionAmbiguity > 3 ? '4' : '_');
+  lcd.print('\'');
+};
+
 
 uint8_t nmeaState = 0;
 char nmeaStr[256]; // NMEA-0183 messages should only be 82 characters, but the NEO-6M sends much longer messages
@@ -624,10 +653,24 @@ void readNmeaRmc() {
 		   rmc.lonDeg, rmc.lonMin, rmc.lonDir,
 		   config.marker, rmc.course, rmc.speed);
 	} else {
-	  snprintf(aprs, 256, "/012058z4700.00N/00700.00Eb000/000");
+	  snprintf(aprs, 256, "/012058z4712.34N/00712.34Eb000/000");
+	}
+	// Insert position ambiguity
+	if (config.positionAmbiguity < 1) {
+	  aprs[10] = aprs[20] = ' ';
+	}
+	if (config.positionAmbiguity < 2) {
+	  aprs[11] = aprs[21] = ' ';
+	}
+	if (config.positionAmbiguity < 3) {
+	  aprs[13] = aprs[23] = ' ';
+	}
+	if (config.positionAmbiguity < 4) {
+	  aprs[14] = aprs[24] = ' ';
 	}
 	memcpy(aprs+34, config.comment, config.commentLen);
 	aprs[34+config.commentLen] = 0;
+	Serial.println(aprs);
 	// AX.25 3.8 - FCS is sent MSB first
 	uint16_t fcs = 0xffff;
 	for (size_t i = 0; i < sizeof(frame); ++i) {
@@ -702,39 +745,50 @@ void setup() {
 
 void loop() {
   readNmeaRmc();
-    if (editingConfig) {
-      editConfig();
-      return;
+  if (editingConfig) {
+    editConfig();
+    return;
+  }
+  if (editingComment) {
+    editComment();
+    return;
+  } 
+  if (editingAmbiguity) {
+    editAmbiguity();
+    return;
+  } 
+  if (abcPressed) {
+    abcPressed = false;
+    page = (page + 1) % 4;
+    lcd.clear();
+  }
+  if (page == 0) {
+    printConfig();
+    if (setPressed) {
+      setPressed = false;
+      editingConfig = true;
+      lcd.blink();
     }
-    if (editingComment) {
-      editComment();
-      return;
-    } 
-    if (abcPressed) {
-      abcPressed = false;
-      page = (page + 1) % 4;
+  } else if (page == 1) {
+    printComment();
+    if (setPressed) {
+      setPressed = false;
+      editingComment = true;
       lcd.clear();
-    }
-    if (page == 0) {
-      printConfig();
-      if (setPressed) {
-	setPressed = false;
-	editingConfig = true;
-	lcd.blink();
-      }
-    } else if (page == 1) {
       printComment();
-      if (setPressed) {
-	setPressed = false;
-	editingComment = true;
-	lcd.clear();
-	lcd.blink();
-      }
-    } else if (page == 2) {
-      printLocation();
-    } else if (page == 3) {
-      printDateTime();
+      lcd.blink();
     }
+  } else if (page == 2) {
+    printLocation();
+    if (setPressed) {
+      setPressed = false;
+      editingAmbiguity = true;
+      lcd.clear();
+      editAmbiguity();
+    }
+  } else if (page == 3) {
+    printDateTime();
+  }
   LowPower.powerDown(SLEEP_8S, ADC_OFF, BOD_OFF);
   if (!abcPressed && !setPressed) {
       off = true;