diff --git a/BaseMQ.cpp b/BaseMQ.cpp
index 7a7f0c7..d289a1b 100644
--- a/BaseMQ.cpp
+++ b/BaseMQ.cpp
@@ -65,7 +65,7 @@ float BaseMQ::readRs() {
   return rs;
 }
 
-int readScaled(float a, float b) {
+unsigned long readScaled(float a, float b) {
   float ratio = readRatio();
   return exp((log(ratio)-b)/a);
 }
diff --git a/BaseMQ.h b/BaseMQ.h
index d830d80..2093b18 100644
--- a/BaseMQ.h
+++ b/BaseMQ.h
@@ -31,7 +31,7 @@ protected:
 	uint8_t _pin;
 	uint8_t _pinHeater;
 	float readRs();
-	int readScaled(float a, float b);
+	unsigned long readScaled(float a, float b);
 	float calculateResistance(int rawAdc);
 	virtual float getRoInCleanAir() const = 0;
 	virtual int getRL() const = 0;