void setup() {
  Serial.begin(115200);
  //set the resolution to 12 bits (0-4096)
  analogReadResolution(12);
}

void loop() {
  // read analog millivolts value
  int analogValue = analogRead(15);
  int analogVolts = analogReadMilliVolts(15);
  //Voltage shift -200mV
  int calVolts = analogVolts - 200;
  
  Serial.printf("ADC analog value = %d\n",analogValue);
  Serial.printf("ADC millivolts value = %d\n",analogVolts);
  Serial.printf("Calibrated value = %d\n",calVolts);
  
  delay(1000); 
}