diff --git a/firmware/v01/v01.ino b/firmware/v01/v01.ino
index ab0efed..284b8a6 100644
--- a/firmware/v01/v01.ino
+++ b/firmware/v01/v01.ino
@@ -123,57 +123,57 @@ void setup() {    // BEGIN SETUP ------------------------------------
 // Timer compare interrupt service routine --------------------------
 ISR(TIMER1_COMPA_vect)
 {
-	if (!rUP)							// If button UP pressed
+	if (!rUP)						// If button UP pressed
 	{
-		if (menuState == 1){}				// Do nothing and leave menuState
-								// as it is (4)
+		if (menuState == 1){}		// Do nothing and leave menuState
+									// as it is (1)
 		else {
 			menuState--;
 		}
-		while (!rUP); 			// Check if button is still pressed do nothing
+		while (!rUP);				// Check if button is still pressed, do nothing
 	}
 
 
-	if (!rDOWN)							// If button DOWN pressed
+	if (!rDOWN)						// If button DOWN pressed
 	{
-		if (menuState == 4){}				// Do nothing and leave menuState
-								// as it is (4)
+		if (menuState == 4){}		// Do nothing and leave menuState
+									// as it is (4)
 		else {
 			menuState++;
 		}
-		while (!rDOWN); 		// Check if button is still pressed do nothing
+		while (!rDOWN);				// Check if button is still pressed, do nothing
 	}
 
 
-	if (!rOK)							// If button OK pressed
+	if (!rOK)						// If button OK pressed
 	{
-		if (menuState == 1)				// and the menuState is 1
+		if (menuState == 1)			// and the menuState is 1
 		{
-			prevMenu = menuState;			// and set prevMenu to 1
-			menuState = 10;				// then reset menuState to 10
+			prevMenu = menuState;	// set prevMenu to 1
+			menuState = 10;			// then reset menuState to 10
 		}
-		else if (menuState == 2)		// If menuState is 2
+		else if (menuState == 2)	// If menuState is 2
 		{
-			prevMenu = menuState;			// and set prevMenu to 2
-			menuState = 11;				// then reset menuState to 11
+			prevMenu = menuState;	// set prevMenu to 2
+			menuState = 11;			// then reset menuState to 11
 		}
-		else if (menuState == 3)		// If menuState is 3
+		else if (menuState == 3)	// If menuState is 3
 		{
-			prevMenu = menuState;			// and set prevMenu to 3
-			menuState = 12;				// then reset menuState to 12
+			prevMenu = menuState;	// set prevMenu to 3
+			menuState = 12;			// then reset menuState to 12
 		}
-		else if (menuState == 4)		// If menuState is 4
+		else if (menuState == 4)	// If menuState is 4
 		{
-			prevMenu = menuState;			// and set prevMenu to 4
-			menuState = 13;				// then reset menuState to 13
+			prevMenu = menuState;	// set prevMenu to 4
+			menuState = 13;			// then reset menuState to 13
 		}
-		while (!rOK); 			// Check if button is still pressed do nothing
+		while (!rOK);				// Check if button is still pressed, do nothing
 	}
 
-	if (!rCANCEL) 						// If button OK pressed
+	if (!rCANCEL)					// If button CANCEL pressed
 	{
-		menuState = prevMenu;
-		while (!rCANCEL); // Check if button is still pressed do nothing
+		menuState = prevMenu;		// set menuState to same value as prevMenu
+		while (!rCANCEL);			// Check if button is still pressed, do nothing
 	}
 
 }
@@ -422,9 +422,9 @@ void read_serial (void)
 		Serial.write(mySerial.read());				// redirect it to USB
 	}
 
-	if (Serial.available())						// If incoming NMEA0183 serial
+	if (Serial.available())							// If incoming USB serial
 	{
-		mySerial.write(Serial.read());				// redirect it to USB
+		mySerial.write(Serial.read());				// redirect it to NMEA0183 serial
 	}
 }
 
@@ -432,7 +432,7 @@ void write_gps (void)
 {
 	// Write NMEA0183 GPS sentence to USB
 	mySerial.print("$GPGGA,090000.10,6350.37829338,N,02225.18272240,W,1,05,2.87,160.00,M,-21.3213,M,,*64");
-	mySerial.println();								// Print on display
+	mySerial.println();								// Send string to NMEA0183 serial
 	delay(100);
 }
 
@@ -440,7 +440,7 @@ void write_hdg (void)
 {
 	// Write NMEA0183 Heading sentence to USB
 	mySerial.print("$HEHDT,268.4,T*27");
-	mySerial.println();								// Print on display
+	mySerial.println();								// Send string to NMEA0183 serial
 	delay(100);
 }
 
@@ -448,6 +448,6 @@ void write_dep (void)
 {
 	// Write NMEA0183 Depth sentence to USB
 	mySerial.print("$SDDBT,0038.0,f,0011.6,M,0006.3,F");
-	mySerial.println();								// Print on display
+	mySerial.println();								// Send string to NMEA0183 serial
 	delay(100);
 }