Clever low voltage monitor (no external components)

I found this clever little snippet of code that will return the supply voltage for the arduino using no external components! Would be great for those lipo projects !!!

http://code.google.com/p/tinkerit/wiki/SecretVoltmeter

Just in case the link vanishes I have copied the code here

long readVcc() {
  long result;
  // Read 1.1V reference against AVcc
  ADMUX = _BV(REFS0) | _BV(MUX3) | _BV(MUX2) | _BV(MUX1);
  delay(2); // Wait for Vref to settle
  ADCSRA |= _BV(ADSC); // Convert
  while (bit_is_set(ADCSRA,ADSC));
  result = ADCL;
  result |= ADCH<<8;
  result = 1126400L / result; // Back-calculate AVcc in mV
  return result;
}

void setup() {
  Serial.begin(9600);
}

void loop() {
  Serial.println( readVcc(), DEC );
  delay(1000);
}

Nothing new. It has been done for decades.