# define CHECK_INTERVAL 50
# define startStopPin 7

# define runningLED     6
# define runningTooLED  5

void setup() {
  Serial.begin(115200);
  Serial.println("Hello World!\n");

  pinMode(startStopPin, INPUT_PULLUP);

  pinMode(runningLED, OUTPUT);
  pinMode(runningTooLED, OUTPUT);
}

bool running;
bool runningToo;
bool haveSaid;

unsigned long onInsant, onSluggush;

void loop()
{
  loopOne();
  loopTwo();

  if (running && runningToo && !haveSaid) {
    Serial.print(" sluggish : ");
    Serial.print(onSluggush - onInsant);
    Serial.println(" milliseconds later.");

    haveSaid = true;
  }

  if (!running && !runningToo) haveSaid = false;
}

void loopOne() {

  static unsigned long tmrCheck;
  static bool startStopStatus;
  static bool previousState = HIGH;

  unsigned long currentMillis = millis();

  if (currentMillis - tmrCheck > CHECK_INTERVAL) {

    startStopStatus = digitalRead(startStopPin);

    if (startStopStatus != previousState) {

      if (previousState == HIGH)
        running = !running;

      if (running) onInsant = currentMillis;

      tmrCheck = currentMillis;
      previousState = startStopStatus;
    }
  }

  digitalWrite(runningLED, running);
}

void loopTwo() {

  static unsigned long tmrCheck;
  static bool startStopStatus;
  static bool previousState = HIGH;

  unsigned long currentMillis = millis();

  if (currentMillis - tmrCheck >= CHECK_INTERVAL) {
    // It's time to check the Start/Stop button!
    startStopStatus = digitalRead(startStopPin);
    // Changed? Toggle the "Running" state
    if (startStopStatus != previousState && previousState) {
      runningToo = !runningToo;

    if (runningToo) onSluggush = currentMillis;

    }
    // Next check
    tmrCheck = currentMillis;
    previousState = startStopStatus;
  }

  digitalWrite(runningTooLED, runningToo);
}