diff --git a/examples/MQ-2/MQ-2.ino b/examples/MQ-2/MQ-2.ino
index 3d0d623..9e8aee1 100644
--- a/examples/MQ-2/MQ-2.ino
+++ b/examples/MQ-2/MQ-2.ino
@@ -25,17 +25,14 @@
 MQUnifiedsensor MQ2(pin, type);
 
 void setup() {
+  //Init serial port
+  Serial.begin(115200);
   //init the sensor
   MQ2.inicializar(); 
 }
 
 void loop() {
-  //Read the sensor
-  int read =  MQ2.readSensor();
-  //Print measurements
-  Serial.print("MQ2: ");
-  Serial.print(read);
-  Serial.println(" PPM");
-  //delay 1s to next measure
-  delay(1000);
+  //Read the sensor and print in serial port
+  int lecture =  MQ2.readSensor("", true);
+  delay(400);
 }
diff --git a/src/MQUnifiedsensor.cpp b/src/MQUnifiedsensor.cpp
index da12b47..6593d73 100644
--- a/src/MQUnifiedsensor.cpp
+++ b/src/MQUnifiedsensor.cpp
@@ -81,14 +81,12 @@ int MQUnifiedsensor::readSensor(String nameLectureRequeired, bool print)
   if(print)
   {
     String nameLecture = getnameLecture();
-  
-    Serial.print("Medicion");
-    Serial.print("(" + nameLecture + "): ");
-    Serial.println(_PPM);
-    Serial.print("Slope: ");
-    Serial.print(String(_m));
-    Serial.print(", B point: ");
-    Serial.println(String(_b));
+    Serial.println("**********************");
+    Serial.println("* Sensor: MQ-" + String(_type));
+    Serial.println("* m =" + String(_m) + " ,b =" + String(_b));
+    Serial.println("* RS/R0 = " + String(_ratio) + " ,Voltaje leido(ADC): " + String(this->getVoltage()));
+    Serial.println("* Lectura(" + nameLecture + ")=" + String(_PPM) + " PPM");
+    Serial.println("**********************");
   }
   return _PPM;
 }
@@ -103,34 +101,20 @@ void MQUnifiedsensor::setSensorCharacteristics(String nameLectureRequeired, bool
   {
     //Set default
     setDefaultGas();
+    //Set ratio in clean air to calc R0
+    setRatioInCleanAir();
     //Put  the default into variable internally used
     nameLectureRequeired = _nameLectureRequeired;
   }
 
   //Dinamic index search
-  if(print)
-  {
-    Serial.println("Busqueda dinamica de los indices");
-  }
   for (int i=0; i<sizeof(_MQ); i++) {
       if (nameLectureRequeired == _MQ[i]) {    //modified here
         _lecturePosInArray = i;
         break;
       }
     }
-  
   //Serial debugging
-  if(print)
-  {
-    String nameLecture = getnameLecture();
-  
-    Serial.print("index in nameLectures: ");
-    Serial.println(_lecturePosInArray);
-    Serial.print("Slope index: ");
-    Serial.println(_lecturePosInArray+1);
-    Serial.print("B point index: ");
-    Serial.println(_lecturePosInArray+2);
-  }
   _m = stringToDouble(_MQ[_lecturePosInArray+1]);
   _b = stringToDouble(_MQ[_lecturePosInArray+2]);
   //Save the name for future calls
@@ -142,13 +126,12 @@ int MQUnifiedsensor::readPPM(int m, int b) {
   */
   double sensor_volt = this->getVoltage();
   double RS_gas; //Define variable for sensor resistance
-  double ratio; //Define variable for ratio
 
   RS_gas = ((5.0 * 10.0) / sensor_volt) - 10.0; //Get value of RS in a gas
 
-  ratio = RS_gas / this->_R0;   // Get ratio RS_gas/RS_air
+  _ratio = RS_gas / this->_R0;   // Get ratio RS_gas/RS_air
 
-  double ppm_log = (log10(ratio) - b) / m; //Get ppm value in linear scale according to the the ratio value
+  double ppm_log = (log10(_ratio) - b) / m; //Get ppm value in linear scale according to the the ratio value
   double ppm = pow(10, ppm_log); //Convert ppm value to log scale
   return floor(ppm);
 }
@@ -158,8 +141,8 @@ double MQUnifiedsensor::calibrate() {
     float R0; //Define variable for R0
     float sensorValue; //Define variable for analog readings
     sensor_volt = this->getVoltage(); //Convert average to voltage
-    RS_air = ((5.0 * 10.0) / sensor_volt) - 10.0; //Calculate RS in fresh air
-    R0 = RS_air / 4.4; //Calculate R0
+    RS_air = (5.0-sensor_volt)/sensor_volt; // omit *RL
+    R0 = RS_air / _ratioInCleanAir; //Calculate R0
     return R0;
 }
 double MQUnifiedsensor::getVoltage() {
@@ -178,7 +161,6 @@ void MQUnifiedsensor::setR0(double R0) {
 }
 void MQUnifiedsensor::setDefaultGas()
 {
-  Serial.println("Carga de los gases por defecto");
     if(_type == 2)
     {
       _nameLectureRequeired = defaultMQ2;
@@ -228,6 +210,57 @@ void MQUnifiedsensor::setDefaultGas()
       _nameLectureRequeired = defaultMQ309;
     }
 }
+void MQUnifiedsensor::setRatioInCleanAir()
+{
+    if(_type == 2)
+    {
+      _ratioInCleanAir = RatioMQ2CleanAir;
+    }
+    else if(_type == 3)
+    {
+      _ratioInCleanAir = RatioMQ3CleanAir;
+    }
+    else if(_type == 4)
+    {
+      _ratioInCleanAir = RatioMQ4CleanAir;
+    }
+    else if(_type == 5)
+    {
+      _ratioInCleanAir = RatioMQ5CleanAir;
+    }
+    else if(_type == 6)
+    {
+      _ratioInCleanAir = RatioMQ6CleanAir;
+    }
+    else if(_type == 7)
+    {
+      _ratioInCleanAir = RatioMQ7CleanAir;
+    }
+    else if(_type == 8)
+    {
+      _ratioInCleanAir = RatioMQ8CleanAir;
+    }
+    else if(_type == 9)
+    {
+      _ratioInCleanAir = RatioMQ9CleanAir;
+    }
+    else if(_type == 131)
+    {
+      _ratioInCleanAir = RatioMQ131CleanAir;
+    }
+    else if(_type == 135)
+    {
+      _ratioInCleanAir = RatioMQ135CleanAir;
+    }
+    else if(_type == 303)
+    {
+      _ratioInCleanAir = RatioMQ303CleanAir;
+    }
+    else if(_type == 309)
+    {
+      _ratioInCleanAir = RatioMQ309CleanAir;
+    }
+}
 double MQUnifiedsensor::stringToDouble(String & str)
 {
   return atof( str.c_str() );
diff --git a/src/MQUnifiedsensor.h b/src/MQUnifiedsensor.h
index ce005c4..46b872c 100644
--- a/src/MQUnifiedsensor.h
+++ b/src/MQUnifiedsensor.h
@@ -21,24 +21,37 @@
 #define defaultMQ303 "Isobutano" //Isobutano
 #define defaultMQ309 "CO" //CO
 
+#define RatioMQ2CleanAir 1
+#define RatioMQ3CleanAir 2
+#define RatioMQ4CleanAir 3
+#define RatioMQ5CleanAir 4
+#define RatioMQ6CleanAir 5
+#define RatioMQ7CleanAir 6
+#define RatioMQ8CleanAir 7
+#define RatioMQ9CleanAir 8
+#define RatioMQ131CleanAir 9
+#define RatioMQ135CleanAir 131
+#define RatioMQ303CleanAir 135
+#define RatioMQ309CleanAir 303
+
 #define ADC_RESOLUTION 10 // for 10bit analog to digital converter.
 #define retries 50
 #define retry_interval 20
 
 //Values consolidated
 /* Gas, Value of m (Slope) and b (Cut on x axis) points */
-const char* const _MQ2[18] = {"H2","-2.2459","2.9845","LPG","-2.2879","2.7901","CO","-2.6208","3.6075","Alcohol","-3.1157","4.5134","Propane","-2.7028","3.5595","Benzene","-2.2879","2.7901"};
-const char* const _MQ3[18] = {"LPG","-3.1851","4.7048","CH4","-17.531","28.785","CO","-4.339","6.4432","Alcohol","-1.435","0.4103","Benzene","-2.7009","0.632","Hexane","-2.7268","3.6299"};
-const char* const _MQ4[15] = {"LPG","-2.5818","3.6303","CH4","0.9873","2.6386","CO","-5.5945","5.6693","Alcohol","-11.89","9.0375","smoke","-11.189","9.0375"};
-const char* const _MQ5[15] = {"H2","-4.368","2.9667","LPG","-2.5723","1.8943","CH4","-2.4438","2.3044","CO","-4.8188","5.2023","Alcohol","-4.419","4.8044"};
-const char* const _MQ6[15] = {"H2","-3.6775","5.0286","LPG","-1.6567","2.8775","CH4","-1","3.301","CO","-12.791","14.523","Alcohol","-5.8057","7.5292"};
-const char* const _MQ7[15] = {"H2","-1.329","1.8864","LPG","-7.8626","9.1056","CH4","-5.4878","8.8387","CO","-1.4065","2.0162","Alcohol","-6.3219","9.924"};
-const char* const _MQ8[15] = {"H2","-0.7152","2.9891","LPG","-3.419","7.3513","CH4","-7.5609","15.243","CO","-7.0753","15.396","Alcohol","-1.7459","4.7575"};
-const char* const _MQ9[9] = {"LPG","-2.2535","2.9855","CH4","-1.6012","3.1476","CO","-1.749","2.827"};
-const char* const _MQ131[9] = {"Nox","-2.7245","3.3004","CL2","-1.0333","1.7117","O3","-1.2037","1.6455"};
-const char* const _MQ135[18] = {"CO","-2.7268","2.301","Alcohol","-2.8608","1.8627","CO2","-3.2819","1.9903","Tolueno","-5.7015","1.1612","NH4","-2.2119","2.0473","Acetona","-5.9682","1.0175"};
-const char* const _MQ303A[9] = {"Iso-butano","-2.3543","1.144","Hydrogeno","-2.4338","0.7558","Ethanol","-2.5597","0.4436"};
-const char* const _MQ309A[12] = {"H2","-2.1311","3.0886","CH4","-1.6554","2.985","CO","-4.7623","6.7413","Alcohol","-3.7686","5.6744"};
+const String _MQ2[18] = {"H2","-2.2459","2.9845","LPG","-2.2879","2.7901","CO","-2.6208","3.6075","Alcohol","-3.1157","4.5134","Propane","-2.7028","3.5595","Benzene","-2.2879","2.7901"};
+const String _MQ3[18] = {"LPG","-3.1851","4.7048","CH4","-17.531","28.785","CO","-4.339","6.4432","Alcohol","-1.435","0.4103","Benzene","-2.7009","0.632","Hexane","-2.7268","3.6299"};
+const String _MQ4[15] = {"LPG","-2.5818","3.6303","CH4","0.9873","2.6386","CO","-5.5945","5.6693","Alcohol","-11.89","9.0375","smoke","-11.189","9.0375"};
+const String _MQ5[15] = {"H2","-4.368","2.9667","LPG","-2.5723","1.8943","CH4","-2.4438","2.3044","CO","-4.8188","5.2023","Alcohol","-4.419","4.8044"};
+const String _MQ6[15] = {"H2","-3.6775","5.0286","LPG","-1.6567","2.8775","CH4","-1","3.301","CO","-12.791","14.523","Alcohol","-5.8057","7.5292"};
+const String _MQ7[15] = {"H2","-1.329","1.8864","LPG","-7.8626","9.1056","CH4","-5.4878","8.8387","CO","-1.4065","2.0162","Alcohol","-6.3219","9.924"};
+const String _MQ8[15] = {"H2","-0.7152","2.9891","LPG","-3.419","7.3513","CH4","-7.5609","15.243","CO","-7.0753","15.396","Alcohol","-1.7459","4.7575"};
+const String _MQ9[9] = {"LPG","-2.2535","2.9855","CH4","-1.6012","3.1476","CO","-1.749","2.827"};
+const String _MQ131[9] = {"Nox","-2.7245","3.3004","CL2","-1.0333","1.7117","O3","-1.2037","1.6455"};
+const String _MQ135[18] = {"CO","-2.7268","2.301","Alcohol","-2.8608","1.8627","CO2","-3.2819","1.9903","Tolueno","-5.7015","1.1612","NH4","-2.2119","2.0473","Acetona","-5.9682","1.0175"};
+const String _MQ303A[9] = {"Iso-butano","-2.3543","1.144","Hydrogeno","-2.4338","0.7558","Ethanol","-2.5597","0.4436"};
+const String _MQ309A[12] = {"H2","-2.1311","3.0886","CH4","-1.6554","2.985","CO","-4.7623","6.7413","Alcohol","-3.7686","5.6744"};
 
 class MQUnifiedsensor
 {
@@ -49,6 +62,7 @@ class MQUnifiedsensor
     void setVoltResolution(float voltaje);
     void setSensorCharacteristics(String nameLectureReqeuired, bool print);
     void setDefaultGas();
+    void setRatioInCleanAir();
     
     int readSensor(String nameLectureRequeired = "", bool print = false);
     int readPPM(int m, int b);
@@ -62,8 +76,8 @@ class MQUnifiedsensor
     
 
   private:
-    int _pin, _type, _PPM, _lecturePosInArray;
-    double _R0, _m, _b;
+    int _pin, _type, _PPM, _lecturePosInArray, _ratioInCleanAir;
+    double RS_air,_R0 = 11.820, _m, _b, _ratio;
     String _MQ[19], _nameLectureRequeired;   
     int VOLT_RESOLUTION  = 5.0; // if 3.3v use 3.3
 };