// Arduino code to print "start" then delay 3 seconds with millis and after delay finish print "done" and the elapsed time. Clear serial monitor before print.

void setup() {
  // initialize serial communication at 9600 bits per second:
  Serial.begin(9600);
}

void loop() {
  // clear the serial monitor by sending a special character:
  Serial.write(12);

  digitalWrite(13, HIGH);
delay(2000);
    digitalWrite(13, LOW);

  // print "start" to the serial monitor:
  Serial.println("start");

  // get the current time in milliseconds:
  unsigned long startTime = millis();

  // wait for 3 seconds using millis():
  while (millis() - startTime < 2000) {
    // do nothing
  }

  // get the elapsed time in milliseconds:
  unsigned long elapsedTime = millis() - startTime;

  // print "done" and the elapsed time to the serial monitor:
  Serial.print("done");
  Serial.print(" in ");
  Serial.print(elapsedTime);
  Serial.println(" milliseconds");
}