diff --git a/ModbusThermometer.cpp b/ModbusThermometer.cpp
index 4d9822b..1992f94 100644
--- a/ModbusThermometer.cpp
+++ b/ModbusThermometer.cpp
@@ -35,7 +35,11 @@ Thermometer thermometer[NUM_OF_CHANNELS];
 LED led;
 Metro secondTick = Metro(1000);
 uint32_t uptimeSeconds = 0;
-bool calibrationDone = false;
+
+
+typedef enum { e_CAL_IDLE, e_CAL_RUNNING, e_CAL_SET, e_CAL_COMPLETE } tCalibrationState;
+
+tCalibrationState calibrationState = e_CAL_IDLE;
 uint16_t calibrationCycleCnt = 0;
 float calibrationValueSum[NUM_OF_CHANNELS];
 
@@ -118,9 +122,32 @@ void loop() {
     }
 	}
 
-  if (((digitalRead(CAL_ENABLE) != 0) && (! calibrationDone)) {
+  if ((digitalRead(CAL_ENABLE) != 0) && 
+      ((digitalRead(CAL_OFFSET_ENABLE) != 0) || (digitalRead(CAL_FACTOR_ENABLE) != 0)) &&
+      (calibrationState != e_CAL_COMPLETE)) {
     led.toggle();
-    calibrationCycleCnt++;
+
+    switch (calibrationState) {
+      case e_CAL_IDLE:
+        calibrationState = e_CAL_RUNNING;
+        break;
+      case e_CAL_RUNNING:
+        calibrationCycleCnt++;
+        for (uint8_t i = 0; i < NUM_OF_CHANNELS; i++) {
+          calibrationValueSum += ads1210[i].getValue();
+        }
+        if (calibrationCycleCnt >= CALIBRATION_CYCLES) {
+          calibrationState = e_CAL_SET;
+        }
+        break;
+      case e_CAL_SET:
+        // calculate and set according to selected calibration mode
+        calibrationState = e_CAL_COMPLETE;
+        break;
+      default:
+        calibrationState = e_CAL_COMPLETE;
+        break;
+    }
   }
 
   if ((digitalRead(CAL_ENABLE) == 0) && (secondTick.check() == 1)) {