double secondsRaw;

double hours;
int hoursToShow;

double minutes;
int minutesToShow;

double seconds;
int secondsToShow;

String timeToPrint;

void setup() {
  Serial.begin(9600);
  Serial.println("BEGIN");
  Serial.println();
}

void loop() {
secondsRaw = millis() / 1000;

hours = fmod(secondsRaw / 3600.0, 1);
hoursToShow = secondsRaw / 3600;
minutes = hours * 3600.0 / 60;
minutesToShow = minutes;
seconds = fmod(minutes, 1);
secondsToShow = seconds * 60;

timeToPrint = String(hoursToShow) + ":" + String(minutesToShow) + ":" + String(secondsToShow);
Serial.println(timeToPrint);

delay(1000);

}