diff --git a/firmware/AVR-Source/Pyr0_Piezo_Sensor_v2.x.x/Pyr0_Piezo_Sensor_v2.x.x.ino b/firmware/AVR-Source/Pyr0_Piezo_Sensor_v2.x.x/Pyr0_Piezo_Sensor_v2.x.x.ino
index fb1ccaf..bd57771 100644
--- a/firmware/AVR-Source/Pyr0_Piezo_Sensor_v2.x.x/Pyr0_Piezo_Sensor_v2.x.x.ino
+++ b/firmware/AVR-Source/Pyr0_Piezo_Sensor_v2.x.x/Pyr0_Piezo_Sensor_v2.x.x.ino
@@ -55,13 +55,14 @@ The gain STATE is representative of these values:
 */
 
 // Configurable settings:
-int GAIN_FACTOR = 2;           // Gain adjustment factor. 0=3x, 1=3.5x, 2=4.33x, 3=6x, 4=11x
+int GAIN_FACTOR = 2;            // Gain adjustment factor. 0=3x, 1=3.5x, 2=4.33x, 3=6x, 4=11x
 #define InitCount 6             // Number of times to blink the LED on start
-int LOOP_DUR = 50;        // duration of time between ADC checks and other loop functions
-int TRG_DUR = 20;             // duration of the Z-axis pulse sent, in ms
+int LOOP_DUR = 50;              // duration of time between ADC checks and other loop functions
+int TRG_DUR = 20;               // duration of the Z-axis pulse sent, in ms
 #define senseThrs 1450
 #define compThrs 2850
-int Hyst = 20;                 // Hysteresis value for ADC measurements
+int Hyst = 20;                  // Hysteresis value for ADC measurements
+long voltMeterConstant = 1125300L; // For fine tuning input voltage sense
 
 /*------------------------------------------------------------*/
 
diff --git a/firmware/AVR-Source/Pyr0_Piezo_Sensor_v2.x.x/pP_function.h b/firmware/AVR-Source/Pyr0_Piezo_Sensor_v2.x.x/pP_function.h
index a1de50a..80a9f80 100644
--- a/firmware/AVR-Source/Pyr0_Piezo_Sensor_v2.x.x/pP_function.h
+++ b/firmware/AVR-Source/Pyr0_Piezo_Sensor_v2.x.x/pP_function.h
@@ -45,7 +45,7 @@ long readVcc() {
 
   long result = (high<<8) | low;
 
-  result = 1125300L / result; // Calculate Vcc (in mV); 1125300 = 1.1*1023*1000
+  result = voltMeterConstant / result; // Calculate Vcc (in mV); 1125300 = 1.1*1023*1000
   return result; // Vcc in millivolts
 }