ADC_MODE(ADC_VCC);  // allows you to monitor the internal VCC level; it varies with WiFi load

int maxProbes=10;

int minV=100000;
int maxV=0;
float sumSquares=0.0;
float sum=0.0;
bool done=false;

void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
  Serial.println();
}

void loop() {

  if (! done) {
    for (int i=0; i<maxProbes; i++) {
      int volts = ESP.getVcc();
      Serial.printf("The internal VCC reads %d\n",volts);
      if (volts < minV) minV=volts;
      if (volts > maxV) maxV=volts;
      sum+=volts;
      sumSquares+=float(volts)*volts;
      delay(1000);
    }
    float avg = sum/maxProbes;
    float var = sumSquares/float(maxProbes) - (avg*avg);
    float std = sqrt(var);
    Serial.printf("Probes: %d, Min: %d, Max: %d, Avg: %.2f, Std: %f Var: %f\n",maxProbes, minV, maxV, avg, std, var);
    done=true;
  }
  else {
    Serial.println("Done");
    delay(10000);
  }
}