diff --git a/IF97.h b/IF97.h
index 28581fa..ebbbd3b 100644
--- a/IF97.h
+++ b/IF97.h
@@ -3919,12 +3919,22 @@ namespace IF97
                                return R2.output(outkey, T, p);  // On saturation curve and need the Vapor phase
                            else
                                return R1.output(outkey, T, p);  // otherwise, use Liquid Region 1
+                           break;
             case REGION_2: if (State == LIQUID)
                                return R1.output(outkey, T, p);  // On saturation curve and need the Liquid phase
                            else
                                return R2.output(outkey, T, p);  // otherwise, use Vapor Region 2
+                           break;
             case REGION_3: return R3.output(outkey, T, p, State);
-            case REGION_4: throw std::invalid_argument("Cannot use Region 4 with T and p as inputs");
+                           break;
+            case REGION_4: if (State == VAPOR) {
+                               return R2.output(outkey, T, p);
+                           } else if (State == LIQUID) {
+                               return R1.output(outkey, T, p);
+                           } else {
+                               throw std::out_of_range("Cannot use Region 4 with T and p as inputs");
+                           }
+                           break;
             case REGION_5: return R5.output(outkey, T, p);
         }
         throw std::out_of_range("Unable to match region");
diff --git a/wrapper/Mathcad/IF97.cpp b/wrapper/Mathcad/IF97.cpp
index 4c9275c..80cf143 100644
--- a/wrapper/Mathcad/IF97.cpp
+++ b/wrapper/Mathcad/IF97.cpp
@@ -23,7 +23,7 @@ enum { MC_STRING = STRING };  // substitute enumeration variable MC_STRING for S
 
 // Mathcad Error Codes
 enum EC  {MUST_BE_REAL = 1, INSUFFICIENT_MEMORY, INTERRUPTED, T_OUT_OF_RANGE, P_OUT_OF_RANGE, SATURATED, NO_SOLUTION_FOUND, 
-          D_OUT_OF_RANGE, H_OUT_OF_RANGE, S_OUT_OF_RANGE, REGION_NOT_FOUND, NUMBER_OF_ERRORS};
+          D_OUT_OF_RANGE, H_OUT_OF_RANGE, S_OUT_OF_RANGE, REGION_NOT_FOUND, UNKNOWN, NUMBER_OF_ERRORS};
 
     // Table of Error Messages
     // These message strings MUST be in the order of the Error Code enumeration above, with the last being a dummy value for error count
@@ -40,6 +40,7 @@ enum EC  {MUST_BE_REAL = 1, INSUFFICIENT_MEMORY, INTERRUPTED, T_OUT_OF_RANGE, P_
         "Enthalpy out of Range",
         "Entropy out of Range",
         "Region not found",
+        "Exception thrown - Error Unknown",
         "Error Count - Not Used"
     };
 
diff --git a/wrapper/Mathcad/includes/cptp.h b/wrapper/Mathcad/includes/cptp.h
index 5d81bc5..9f2b6a9 100644
--- a/wrapper/Mathcad/includes/cptp.h
+++ b/wrapper/Mathcad/includes/cptp.h
@@ -21,8 +21,12 @@ LRESULT  if97_CpTP(
     catch (const std::out_of_range& e) { 
         if (e.what()[0] == 'T') 
             return MAKELRESULT(T_OUT_OF_RANGE,1);
-        else // (e.what == "P")
+        else if (e.what()[0] == 'P')
             return MAKELRESULT(P_OUT_OF_RANGE,2);
+        else if (e.what()[0] == 'C')
+            return MAKELRESULT(SATURATED,1);
+        else
+            return MAKELRESULT(UNKNOWN,1);
     }
     catch (const std::logic_error&) {
         return MAKELRESULT(NO_SOLUTION_FOUND,1);
diff --git a/wrapper/Mathcad/includes/cvtp.h b/wrapper/Mathcad/includes/cvtp.h
index 796f6ad..8b95bd7 100644
--- a/wrapper/Mathcad/includes/cvtp.h
+++ b/wrapper/Mathcad/includes/cvtp.h
@@ -21,8 +21,12 @@ LRESULT  if97_CvTP(
     catch (const std::out_of_range& e) { 
         if (e.what()[0] == 'T') 
             return MAKELRESULT(T_OUT_OF_RANGE,1);
-        else // (e.what == "P")
+        else if (e.what()[0] == 'P')
             return MAKELRESULT(P_OUT_OF_RANGE,2);
+        else if (e.what()[0] == 'C')
+            return MAKELRESULT(SATURATED,1);
+        else
+            return MAKELRESULT(UNKNOWN,1);
     }
     catch (const std::logic_error&) {
         return MAKELRESULT(NO_SOLUTION_FOUND,1);
diff --git a/wrapper/Mathcad/includes/htp.h b/wrapper/Mathcad/includes/htp.h
index 9b98ae8..f7e5e42 100644
--- a/wrapper/Mathcad/includes/htp.h
+++ b/wrapper/Mathcad/includes/htp.h
@@ -21,8 +21,12 @@ LRESULT  if97_HTP(
     catch (const std::out_of_range& e) { 
         if (e.what()[0] == 'T') 
             return MAKELRESULT(T_OUT_OF_RANGE,1);
-        else // (e.what == "P")
+        else if (e.what()[0] == 'P')
             return MAKELRESULT(P_OUT_OF_RANGE,2);
+        else if (e.what()[0] == 'C')
+            return MAKELRESULT(SATURATED,1);
+        else
+            return MAKELRESULT(UNKNOWN,1);
     }
     catch (const std::logic_error&) {
         return MAKELRESULT(NO_SOLUTION_FOUND,1);
diff --git a/wrapper/Mathcad/includes/ktp.h b/wrapper/Mathcad/includes/ktp.h
index ceaffd6..1afde33 100644
--- a/wrapper/Mathcad/includes/ktp.h
+++ b/wrapper/Mathcad/includes/ktp.h
@@ -21,8 +21,12 @@ LRESULT  if97_KTP(
     catch (const std::out_of_range& e) { 
         if (e.what()[0] == 'T') 
             return MAKELRESULT(T_OUT_OF_RANGE,1);
-        else // (e.what == "P")
+        else if (e.what()[0] == 'P')
             return MAKELRESULT(P_OUT_OF_RANGE,2);
+        else if (e.what()[0] == 'C')
+            return MAKELRESULT(SATURATED,1);
+        else
+            return MAKELRESULT(UNKNOWN,1);
     }
     catch (const std::logic_error&) {
         return MAKELRESULT(NO_SOLUTION_FOUND,1);
diff --git a/wrapper/Mathcad/includes/mutp.h b/wrapper/Mathcad/includes/mutp.h
index 9f5d8c7..cb908e3 100644
--- a/wrapper/Mathcad/includes/mutp.h
+++ b/wrapper/Mathcad/includes/mutp.h
@@ -21,8 +21,12 @@ LRESULT  if97_MUTP(
     catch (const std::out_of_range& e) { 
         if (e.what()[0] == 'T') 
             return MAKELRESULT(T_OUT_OF_RANGE,1);
-        else // (e.what == "P")
+        else if (e.what()[0] == 'P')
             return MAKELRESULT(P_OUT_OF_RANGE,2);
+        else if (e.what()[0] == 'C')
+            return MAKELRESULT(SATURATED,1);
+        else
+            return MAKELRESULT(UNKNOWN,1);
     }
     catch (const std::logic_error&) {
         return MAKELRESULT(NO_SOLUTION_FOUND,1);
diff --git a/wrapper/Mathcad/includes/prtp.h b/wrapper/Mathcad/includes/prtp.h
index 206075b..dbbb2a2 100644
--- a/wrapper/Mathcad/includes/prtp.h
+++ b/wrapper/Mathcad/includes/prtp.h
@@ -21,8 +21,12 @@ LRESULT  if97_PRTP(
     catch (const std::out_of_range& e) { 
         if (e.what()[0] == 'T') 
             return MAKELRESULT(T_OUT_OF_RANGE,1);
-        else // (e.what == "P")
+        else if (e.what()[0] == 'P')
             return MAKELRESULT(P_OUT_OF_RANGE,2);
+        else if (e.what()[0] == 'C')
+            return MAKELRESULT(SATURATED,1);
+        else
+            return MAKELRESULT(UNKNOWN,1);
     }
     catch (const std::logic_error&) {
         return MAKELRESULT(NO_SOLUTION_FOUND,1);
diff --git a/wrapper/Mathcad/includes/rhotp.h b/wrapper/Mathcad/includes/rhotp.h
index efdc668..76a4da2 100644
--- a/wrapper/Mathcad/includes/rhotp.h
+++ b/wrapper/Mathcad/includes/rhotp.h
@@ -22,8 +22,12 @@ LRESULT  if97_RhoTP(
     catch (const std::out_of_range& e) { 
         if (e.what()[0] == 'T') 
             return MAKELRESULT(T_OUT_OF_RANGE,1);
-        else // (e.what == "P")
+        else if (e.what()[0] == 'P')
             return MAKELRESULT(P_OUT_OF_RANGE,2);
+        else if (e.what()[0] == 'C')
+            return MAKELRESULT(SATURATED,1);
+        else
+            return MAKELRESULT(UNKNOWN,1);
     }
     catch (const std::logic_error&) {
         return MAKELRESULT(NO_SOLUTION_FOUND,1);
diff --git a/wrapper/Mathcad/includes/stp.h b/wrapper/Mathcad/includes/stp.h
index 0aefb92..16e5884 100644
--- a/wrapper/Mathcad/includes/stp.h
+++ b/wrapper/Mathcad/includes/stp.h
@@ -21,8 +21,12 @@ LRESULT  if97_STP(
     catch (const std::out_of_range& e) { 
         if (e.what()[0] == 'T') 
             return MAKELRESULT(T_OUT_OF_RANGE,1);
-        else // (e.what == "P")
+        else if (e.what()[0] == 'P')
             return MAKELRESULT(P_OUT_OF_RANGE,2);
+        else if (e.what()[0] == 'C')
+            return MAKELRESULT(SATURATED,1);
+        else
+            return MAKELRESULT(UNKNOWN,1);
     }
     catch (const std::logic_error&) {
         return MAKELRESULT(NO_SOLUTION_FOUND,1);
diff --git a/wrapper/Mathcad/includes/utp.h b/wrapper/Mathcad/includes/utp.h
index 10d3dc0..902da26 100644
--- a/wrapper/Mathcad/includes/utp.h
+++ b/wrapper/Mathcad/includes/utp.h
@@ -21,8 +21,12 @@ LRESULT  if97_UTP(
     catch (const std::out_of_range& e) { 
         if (e.what()[0] == 'T') 
             return MAKELRESULT(T_OUT_OF_RANGE,1);
-        else // (e.what == "P")
+        else if (e.what()[0] == 'P')
             return MAKELRESULT(P_OUT_OF_RANGE,2);
+        else if (e.what()[0] == 'C')
+            return MAKELRESULT(SATURATED,1);
+        else
+            return MAKELRESULT(UNKNOWN,1);
     }
     catch (const std::logic_error&) {
         return MAKELRESULT(NO_SOLUTION_FOUND,1);
diff --git a/wrapper/Mathcad/includes/vtp.h b/wrapper/Mathcad/includes/vtp.h
index 7a4cbbe..de446b7 100644
--- a/wrapper/Mathcad/includes/vtp.h
+++ b/wrapper/Mathcad/includes/vtp.h
@@ -22,8 +22,12 @@ LRESULT  if97_VTP(
     catch (const std::out_of_range &e) { 
         if (e.what()[0] == 'T') 
             return MAKELRESULT(T_OUT_OF_RANGE,1);
-        else // (e.what == "P")
+        else if (e.what()[0] == 'P')
             return MAKELRESULT(P_OUT_OF_RANGE,2);
+        else if (e.what()[0] == 'C')
+            return MAKELRESULT(SATURATED,1);
+        else
+            return MAKELRESULT(UNKNOWN,1);
     }
     catch (const std::logic_error& ) {
         return MAKELRESULT(NO_SOLUTION_FOUND,1);
diff --git a/wrapper/Mathcad/includes/wtp.h b/wrapper/Mathcad/includes/wtp.h
index fa65986..92f5493 100644
--- a/wrapper/Mathcad/includes/wtp.h
+++ b/wrapper/Mathcad/includes/wtp.h
@@ -21,8 +21,12 @@ LRESULT  if97_WTP(
     catch (const std::out_of_range& e) { 
         if (e.what()[0] == 'T') 
             return MAKELRESULT(T_OUT_OF_RANGE,1);
-        else // (e.what == "P")
+        else if (e.what()[0] == 'P')
             return MAKELRESULT(P_OUT_OF_RANGE,2);
+        else if (e.what()[0] == 'C')
+            return MAKELRESULT(SATURATED,1);
+        else
+            return MAKELRESULT(UNKNOWN,1);
     }
     catch (const std::logic_error&) {
         return MAKELRESULT(NO_SOLUTION_FOUND,1);