Index: firmware/App/Services/TxParams.c
===================================================================
diff -u -rd495985858b3ef51b695a44ceedf6c13a8edb821 -r69c276212d96dbf22e4684e8d95b087ae7a9d11b
--- firmware/App/Services/TxParams.c	(.../TxParams.c)	(revision d495985858b3ef51b695a44ceedf6c13a8edb821)
+++ firmware/App/Services/TxParams.c	(.../TxParams.c)	(revision 69c276212d96dbf22e4684e8d95b087ae7a9d11b)
@@ -128,8 +128,8 @@
     { CRITICAL_DATA_TYPE_F32, {.sFlt=0.0},  {.sFlt=3.0},  {.sFlt=0.0}  }, // TREATMENT_PARAM_HEPARIN_DELIVERY_RATE
     { CRITICAL_DATA_TYPE_F32, {.sFlt=35.0}, {.sFlt=38.0}, {.sFlt=37.0} }, // TREATMENT_PARAM_DIALYSATE_TEMPERATURE
     { CRITICAL_DATA_TYPE_F32, {.sFlt=0.10}, {.sFlt=0.20}, {.sFlt=0.20} }, // TREATMENT_PARAM_ACID_CONCENTRATE_CONV_FACTOR  // TODO
-    { CRITICAL_DATA_TYPE_F32, {.sFlt=50.0}, {.sFlt=900.0},{.sFlt=50.0} }, // TREATMENT_PARAM_PRE_WEIGHT
-    { CRITICAL_DATA_TYPE_F32, {.sFlt=50.0}, {.sFlt=900.0},{.sFlt=50.0} }, // TREATMENT_PARAM_EST_TARGET_WEIGHT
+    { CRITICAL_DATA_TYPE_F32, {.sFlt=2.0},  {.sFlt=500.0},{.sFlt=50.0} }, // TREATMENT_PARAM_PRE_WEIGHT
+    { CRITICAL_DATA_TYPE_F32, {.sFlt=2.0},  {.sFlt=500.0},{.sFlt=50.0} }, // TREATMENT_PARAM_EST_TARGET_WEIGHT
     { CRITICAL_DATA_TYPE_F32, {.sFlt=0.0},  {.sFlt=8.0},  {.sFlt=0.0}  }, // TREATMENT_PARAM_UF_VOLUME
 };
 
@@ -733,32 +733,36 @@
     targetWeight = stagedParams[ TREATMENT_PARAM_EST_TARGET_WEIGHT ].sFlt;
     uFVolumeL = stagedParams[ TREATMENT_PARAM_UF_VOLUME ].sFlt;
 
-    // TODO add check to calculate UF volume from weights. near zero check for weight is done in range check.
-    if ( preWeight > NEARLY_ZERO && targetWeight > NEARLY_ZERO && preWeight >= targetWeight)
+    if ( ( preWeight > NEARLY_ZERO ) && ( targetWeight > NEARLY_ZERO ) && ( preWeight >= targetWeight ) )
     {
         // Weights are valid - Calculate UF volume
         derivedUFVolumeL = preWeight - targetWeight;
-        if ( uFVolumeL <= NEARLY_ZERO && derivedUFVolumeL > NEARLY_ZERO )
+        if ( uFVolumeL < NEARLY_ZERO && derivedUFVolumeL > NEARLY_ZERO )
         {
             // Update UF volume with calculated UF volume
             stagedParams[ TREATMENT_PARAM_UF_VOLUME ].sFlt = derivedUFVolumeL;
             uFVolumeL = derivedUFVolumeL;
+            result = TRUE;
         }
         // case where UF volume is non-zero and provided weights
         else
         {
             reasons[ TREATMENT_PARAM_PRE_WEIGHT ] = REQUEST_REJECT_REASON_INVALID_PATIENT_WEIGHTS;
             reasons[ TREATMENT_PARAM_EST_TARGET_WEIGHT ] = REQUEST_REJECT_REASON_INVALID_PATIENT_WEIGHTS;
-            result = FALSE;
+            reasons[ TREATMENT_PARAM_UF_VOLUME ] = REQUEST_REJECT_REASON_UF_VOL_AND_WEIGHTS_INCONSISTENT;
             validWeights = FALSE;
         }
     }
-    // if weights are invalid
+    // provided a non-zero UF volume instead of weights
+    else if ( ( uFVolumeL > NEARLY_ZERO ) && ( preWeight < NEARLY_ZERO ) && ( targetWeight < NEARLY_ZERO ) )
+    {
+        result = TRUE;
+    }
+    // weights are invalid
     else
     {
         reasons[ TREATMENT_PARAM_PRE_WEIGHT ] = REQUEST_REJECT_REASON_INVALID_PATIENT_WEIGHTS;
         reasons[ TREATMENT_PARAM_EST_TARGET_WEIGHT ] = REQUEST_REJECT_REASON_INVALID_PATIENT_WEIGHTS;
-        result = FALSE;
         validWeights = FALSE;
     }
 
@@ -791,6 +795,7 @@
     }
     else
     {
+        result = FALSE;
         reasons[ TREATMENT_PARAM_UF_VOLUME ] = REQUEST_REJECT_REASON_UF_VOLUME_OUT_OF_RANGE;
     }