Index: firmware/App/Services/Reservoirs.c
===================================================================
diff -u -recc3eef231cd2527274969e057d9b4763caa273f -re7e9ea67b63911dc9d8d46166fdd09e102111e3f
--- firmware/App/Services/Reservoirs.c	(.../Reservoirs.c)	(revision ecc3eef231cd2527274969e057d9b4763caa273f)
+++ firmware/App/Services/Reservoirs.c	(.../Reservoirs.c)	(revision e7e9ea67b63911dc9d8d46166fdd09e102111e3f)
@@ -8,7 +8,7 @@
 * @file    Reservoirs.c
 *
 * @author  (last)      Dara Navaei
-* @date    (last)      08-Feb-2023
+* @date    (last)      07-Mar-2023
 *
 * @author  (original)  Sean
 * @date    (original)  18-Mar-2020
@@ -73,6 +73,7 @@
     F32 tempRsrvr0ActualTrimmer;                                                                  ///< Temperature actual reservoir in C.
     F32 tempFillMixAvgTrimmer;                                                                    ///< Temperature fill mix average trimmer in C.
     F32 tempRsrvrEndFillTrimmer;                                                                  ///< Temperature reservoir end fill trimmer in C.
+    BOOL usePriTargetTempEquation;                                                                ///< Use primary heater target temperature enquation flag.
 } HEATERS_TEMPERATURE_CALC_DATA_T;
 
 /// Reservoirs previous status
@@ -624,6 +625,7 @@
     heatersTempCalc.timeReservoirFillMS        = params.timeReservoirFillMS;
     heatersTempCalc.tempTargetTrimmer          = params.trimmerTargetTemperature;
     heatersTempCalc.flowTargetDialysateLPM     = params.dialysateFlowLPM;
+    heatersTempCalc.usePriTargetTempEquation   = params.usePriTargetTempEquation;
 
     // Check if this is the first time that the dialysate heating parameters are set in DG
     if ( TRUE == isThisTheFirstCycle )
@@ -643,41 +645,54 @@
  *************************************************************************/
 F32 getPrimaryHeaterTargetTemperature( void )
 {
-    // TODO once the equations are solidified, add the equations as comments to the lines
-    F32 tempTarget       = 0.0;
-    F32 priTargetTemp    = 0.0;
+    F32 tempTargetC      = heatersTempCalc.tempTargetTrimmer;
+    F32 priTargetTempC   = 0.0F;
     F32 targetFillVolML  = getTargetFillVolumeML();
-    F32 UFTimeConstant   = 0.0;
+    F32 UFTimeConstant   = 0.0F;
     F32 tempLastFill     = getLastFillTemperature();
     F32 UFTauCPerMS      = heatingConstsCalRecord.ultrafilterTempTauCPerMin / ( SEC_PER_MIN * MS_PER_SECOND );
     F32 RsrvrTauCPerMS   = heatingConstsCalRecord.reservoirTempTauCPerMin / ( SEC_PER_MIN * MS_PER_SECOND );
     F32 targetROFlowLPM  = getTargetROPumpFlowRateLPM();
-    F32 tgtAicdFlowLPM   = getConcentratePumpTargetFlowMLPM( CONCENTRATEPUMPS_CP1_ACID ) / ML_PER_LITER;
+    F32 tgtAcidFlowLPM   = getConcentratePumpTargetFlowMLPM( CONCENTRATEPUMPS_CP1_ACID ) / ML_PER_LITER;
     F32 tgtBicarbFlowLPM = getConcentratePumpTargetFlowMLPM( CONCENTRATEPUMPS_CP2_BICARB ) / ML_PER_LITER;
-    F32 tgtTotalFlowLPM  = targetROFlowLPM + tgtAicdFlowLPM + tgtBicarbFlowLPM;
+    F32 tgtTotalFlowLPM  = targetROFlowLPM + tgtAcidFlowLPM + tgtBicarbFlowLPM;
 
-    if ( FALSE == isThisTheFirstFill() )
+    if ( TRUE == heatersTempCalc.usePriTargetTempEquation )
     {
-        F32 tempTargetNumerator;
-        F32 targetTempDenominator;
-        F32 tempReservoirUse;
+        if ( FALSE == isThisTheFirstFill() )
+        {
+            F32 tempTargetNumerator;
+            F32 tempTargetDenominator;
+            F32 tempReservoirUse;
 
-        tempReservoirUse                     = heatersTempCalc.tempTargetTrimmer + RESERVOIR_EXTRA_TEMPERATURE;
-        heatersTempCalc.tempReservoirEndFill = tempReservoirUse - ( heatersTempCalc.timeReservoirFill2SwitchMS * RsrvrTauCPerMS );
-        heatersTempCalc.tempReservoir0       = heatersTempCalc.tempReservoirEndFill - ( ( heatersTempCalc.timeReservoirFillMS * HALF ) * RsrvrTauCPerMS );
+            /*
+             * 1. T_rsrvr_use      = T_target
+             * 2. T_rsrvr_end_fill = T_rsrvr_use - (t_rsrvr_fill_2_switch * Tau_rsrvr)
+             * 3. T_rsrvr_0        = T_rsrvr_end_fill - (t_rsrvr_fill/2 * Tau_rsrvr)
+             * 4. T_UF_fill        = T_last_fill + [(t_rsrvr_cycle - t_rsrvr_fill) * Tau_UF]
+             * 5. T_numerator      = T_rsrvr_0 - [(V_UF / V_fill) * T_UF_fill]
+             * 6. T_denominator    = (V_fill - V_UF) / V_fill
+             * 7. T_mix_target     = T_numerator / T_denominator
+             * 8. T_primary_target = T_mix_target * (Q_total / Q_RO) - (Q_acid / Q_RO) * T_acid - (Q_bicarb / Q_RO) * T_bicarb
+             */
 
-        heatersTempCalc.timeUFDecayMS        = (F32)heatersTempCalc.timeReservoirCycleMS - heatersTempCalc.timeReservoirFillMS;
-        UFTimeConstant                       = heatersTempCalc.timeUFDecayMS * UFTauCPerMS;
-        heatersTempCalc.tempUFFill           = tempLastFill + UFTimeConstant;
+            tempReservoirUse                     = heatersTempCalc.tempTargetTrimmer;
+            heatersTempCalc.tempReservoirEndFill = tempReservoirUse - ( heatersTempCalc.timeReservoirFill2SwitchMS * RsrvrTauCPerMS );
+            heatersTempCalc.tempReservoir0       = heatersTempCalc.tempReservoirEndFill - ( ( heatersTempCalc.timeReservoirFillMS * HALF ) * RsrvrTauCPerMS );
 
-        tempTargetNumerator                  = heatersTempCalc.tempReservoir0 - ( ( heatingConstsCalRecord.ultrafilterVolmL / targetFillVolML ) * heatersTempCalc.tempUFFill );
-        targetTempDenominator                = ( ( targetFillVolML - heatingConstsCalRecord.ultrafilterVolmL ) / targetFillVolML );
-        tempTarget                           = tempTargetNumerator / targetTempDenominator;
+            heatersTempCalc.timeUFDecayMS        = (F32)heatersTempCalc.timeReservoirCycleMS - heatersTempCalc.timeReservoirFillMS;
+            UFTimeConstant                       = heatersTempCalc.timeUFDecayMS * UFTauCPerMS;
+            heatersTempCalc.tempUFFill           = tempLastFill + UFTimeConstant;
+
+            tempTargetNumerator                  = heatersTempCalc.tempReservoir0 - ( ( heatingConstsCalRecord.ultrafilterVolmL / targetFillVolML ) * heatersTempCalc.tempUFFill );
+            tempTargetDenominator                = ( ( targetFillVolML - heatingConstsCalRecord.ultrafilterVolmL ) / targetFillVolML );
+            tempTargetC                          = tempTargetNumerator / tempTargetDenominator;
+        }
+        else
+        {
+            tempTargetC                          = heatersTempCalc.tempTargetTrimmer + RESERVOIR_EXTRA_TEMPERATURE;
+        }
     }
-    else
-    {
-        tempTarget                           = heatersTempCalc.tempTargetTrimmer + RESERVOIR_EXTRA_TEMPERATURE;
-    }
 
     if ( targetROFlowLPM > 0 )
     {
@@ -689,17 +704,17 @@
             // the target temperature is calculated by estimating the temperature of the dialysates and volume that is being mixed into the RO water
             F32 acidTemperature   = acidConcentrateCalRecord.acidConcentrate[ CAL_DATA_ACID_CONCENTRATE_1 ].acidBottleTemperature;
             F32 bicarbTemperature = bicarbConcentrateCalRecord.bicarbConcentrate[ CAL_DATA_BICARB_CONCENTRATE_1 ].bicarbBottleTemperature;
-            priTargetTemp         = ( tempTarget * ( tgtTotalFlowLPM / targetROFlowLPM ) ) - ( acidTemperature * ( tgtAicdFlowLPM / targetROFlowLPM ) ) -
+            priTargetTempC        = ( tempTargetC * ( tgtTotalFlowLPM / targetROFlowLPM ) ) - ( acidTemperature * ( tgtAcidFlowLPM / targetROFlowLPM ) ) -
                                     ( bicarbTemperature * ( tgtBicarbFlowLPM / targetROFlowLPM ) );
         }
         else
 #endif
         {
-            priTargetTemp = tempTarget;
+            priTargetTempC = tempTargetC;
         }
     }
 
-    return priTargetTemp;
+    return priTargetTempC;
 }
 
 /*********************************************************************//**