diff --git a/src/MQUnifiedsensor.cpp b/src/MQUnifiedsensor.cpp
index 56ce43d..7794a3d 100644
--- a/src/MQUnifiedsensor.cpp
+++ b/src/MQUnifiedsensor.cpp
@@ -60,9 +60,10 @@ void MQUnifiedsensor::setR0(double R0) {
   this->_R0 = R0;
 }
 
-String MQUnifiedsensor::readSensor(String nameLectureRequeired = "")
+int MQUnifiedsensor::readSensor(String nameLectureRequeired = "")
 {
   setSensorCharacteristics(nameLectureRequeired);
+  return readPPM(_m, _b);
 }
 
 void MQUnifiedsensor::setSensorCharacteristics(String nameLectureRequeired)
diff --git a/src/MQUnifiedsensor.h b/src/MQUnifiedsensor.h
index 0f1a57d..dfba88e 100644
--- a/src/MQUnifiedsensor.h
+++ b/src/MQUnifiedsensor.h
@@ -14,7 +14,7 @@ class MQUnifiedsensor
     void setR0(double R0);
     void setSensorCharacteristics(int MQ[38], String nameLectureReqeuired);
     
-    String readSensor(String nameLectureReqeuired = "");
+    int readSensor(String nameLectureReqeuired = "");
     int readPPM(int m, int b);
 
     /**
@@ -43,6 +43,8 @@ class MQUnifiedsensor
     MQ136 - Hydrogen Sulfide gas
     MQ137 - Ammonia
     MQ138 - Benzene, Toluene, Alcohol, Acetone, Propane, Formaldehyde gas, Hydrogen
+    MQ303A - Isobutano
+    MQ309A - Monoxide
     */
     
     /* Index definitions and header names*/