Index: firmware/App/Modes/Prime.c
===================================================================
diff -u -r24237b8f12f5bb4c9cfa8c51b3b1a92d2d692631 -r11d3b6b7d4ae9f5822998abd4f94792f2d9e1714
--- firmware/App/Modes/Prime.c	(.../Prime.c)	(revision 24237b8f12f5bb4c9cfa8c51b3b1a92d2d692631)
+++ firmware/App/Modes/Prime.c	(.../Prime.c)	(revision 11d3b6b7d4ae9f5822998abd4f94792f2d9e1714)
@@ -96,7 +96,7 @@
 static U32 loadcellSteadyVolumeStartTime;                                                       ///< Load cell steady volume starting time.
 static BOOL runBloodCircuitPrimeAgain;                                                          ///< Flag indicates HD should run blood circuit prime once more time.
 static F32 loadcellReadings[ CIRC_BUF_SIZE ];                                                   ///< Storage for 10 seconds of load cell weight readings.
-static U32 iteration;                                                                           ///< Use to calculate the write and the read index of the circular buffer.
+static U32 currentBufIndex;                                                                        ///< Use to calculate the write and the read index of the circular buffer.
 
 // ********** private function prototypes **********
 
@@ -610,13 +610,13 @@
             setValvePosition( VBV, VALVE_POSITION_C_CLOSE );
             setValveAirTrap( STATE_CLOSED );
 
-            iteration = 0;    // initialize to zero before use
             U32 bufIndex;
             for ( bufIndex = 0; bufIndex < CIRC_BUF_SIZE; bufIndex++ )
             {
                 loadcellReadings[ bufIndex ] = getLoadCellWeight( LOAD_CELL_RESERVOIR_1_PRIMARY );
             }
 
+            currentBufIndex = 0;    // initialize circular buffer read/write index
             primeDialysateBypassStartTime = getMSTimerCount();
             loadcellSteadyVolumeStartTime = getMSTimerCount();
 
@@ -652,10 +652,10 @@
     if ( TRUE == didTimeout( loadcellSteadyVolumeStartTime, LOAD_CELL_STEADY_VOLUME_SAMPLING_TIME ) )
     {
         F32 const currentLoadCellValue = getLoadCellWeight( LOAD_CELL_RESERVOIR_1_PRIMARY );
-        F32 const previousLoadCellValue = loadcellReadings[ iteration % CIRC_BUF_SIZE ];
+        F32 const previousLoadCellValue = loadcellReadings[ currentBufIndex % CIRC_BUF_SIZE ];
         F32 const loadcellDelta = fabs( currentLoadCellValue - previousLoadCellValue );  // delta of the current (now) and the previous (10 seconds ago)
-        loadcellReadings[ ( iteration + MAX_BUF_INDEX ) % CIRC_BUF_SIZE ] = currentLoadCellValue;
-        iteration++;
+        loadcellReadings[ currentBufIndex % CIRC_BUF_SIZE ] = currentLoadCellValue;
+        currentBufIndex++;
 
         if ( ( loadcellDelta < LOAD_CELL_VOLUME_NOISE_TOLERANCE  ) &&
              ( currentLoadCellValue < ( PRIME_DIALYZER_BYPASS_EXPECTED_VOLUME + PRIME_EXPECTED_VOLUME_TOLERANCE ) ) &&  // check the steady state volume of R1
@@ -720,13 +720,14 @@
             setDialInPumpTargetFlowRate( DIALYSATE_PUMP_PRIME_FLOW_RATE_ML_MIN, MOTOR_DIR_FORWARD, PUMP_CONTROL_MODE_OPEN_LOOP );
             setDialOutPumpTargetRate( DIALYSATE_PUMP_PRIME_FLOW_RATE_ML_MIN, MOTOR_DIR_FORWARD, PUMP_CONTROL_MODE_OPEN_LOOP );
 
-            iteration = 0;    // initialize to zero before use
             U32 bufIndex;
             for ( bufIndex = 0; bufIndex < CIRC_BUF_SIZE; bufIndex++ )
             {
                 loadcellReadings[ bufIndex ] = getLoadCellWeight( LOAD_CELL_RESERVOIR_2_PRIMARY );
             }
 
+            currentBufIndex = 0;    // initialize circular buffer read/write index
+
             loadcellSteadyVolumeStartTime   = getMSTimerCount();
             primeDialysateDialyzerStartTime = getMSTimerCount();
             state = HD_PRIME_DIALYSATE_DIALYZER_STATE;
@@ -757,10 +758,10 @@
     if ( TRUE == didTimeout( loadcellSteadyVolumeStartTime, LOAD_CELL_STEADY_VOLUME_SAMPLING_TIME ) )
     {
         F32 const currentLoadCellValue = getLoadCellWeight( LOAD_CELL_RESERVOIR_2_PRIMARY );
-        F32 const previousLoadCellValue = loadcellReadings[ iteration % CIRC_BUF_SIZE ];
+        F32 const previousLoadCellValue = loadcellReadings[ currentBufIndex % CIRC_BUF_SIZE ];
         F32 const loadcellDelta = fabs( currentLoadCellValue - previousLoadCellValue );
-        loadcellReadings[ ( iteration + MAX_BUF_INDEX ) % CIRC_BUF_SIZE ] = currentLoadCellValue;
-        iteration++;
+        loadcellReadings[ currentBufIndex  % CIRC_BUF_SIZE ] = currentLoadCellValue;
+        currentBufIndex++;
 
         if ( ( loadcellDelta < LOAD_CELL_VOLUME_NOISE_TOLERANCE  ) &&
              ( currentLoadCellValue < ( PRIME_DIALYZER_EXPECTED_VOLUME + PRIME_EXPECTED_VOLUME_TOLERANCE ) ) &&  // check the steady state volume of R2