diff --git a/src/com/bytezone/diskbrowser/visicalc/Abs.java b/src/com/bytezone/diskbrowser/visicalc/Abs.java
index 1a719e4..4c8139d 100644
--- a/src/com/bytezone/diskbrowser/visicalc/Abs.java
+++ b/src/com/bytezone/diskbrowser/visicalc/Abs.java
@@ -8,6 +8,8 @@ public class Abs extends Function
   {
     super (cell, text);
 
+    assert text.startsWith ("@ABS(") : text;
+
     source = new Expression (parent, cell, functionText);
     values.add (source);
   }
diff --git a/src/com/bytezone/diskbrowser/visicalc/Acos.java b/src/com/bytezone/diskbrowser/visicalc/Acos.java
index 9a81a4e..a80309c 100644
--- a/src/com/bytezone/diskbrowser/visicalc/Acos.java
+++ b/src/com/bytezone/diskbrowser/visicalc/Acos.java
@@ -8,6 +8,8 @@ public class Acos extends Function
   {
     super (cell, text);
 
+    assert text.startsWith ("@ACOS(") : text;
+
     v = new Expression (parent, cell, functionText).reduce ();
     valueType = ValueType.VALUE;
   }
diff --git a/src/com/bytezone/diskbrowser/visicalc/And.java b/src/com/bytezone/diskbrowser/visicalc/And.java
index bb4334c..b718a7d 100644
--- a/src/com/bytezone/diskbrowser/visicalc/And.java
+++ b/src/com/bytezone/diskbrowser/visicalc/And.java
@@ -11,6 +11,8 @@ class And extends Function
   {
     super (cell, text);
 
+    assert text.startsWith ("@AND(") : text;
+
     String remainder = functionText;
     while (true)
     {
diff --git a/src/com/bytezone/diskbrowser/visicalc/Asin.java b/src/com/bytezone/diskbrowser/visicalc/Asin.java
index a91f883..89ea385 100644
--- a/src/com/bytezone/diskbrowser/visicalc/Asin.java
+++ b/src/com/bytezone/diskbrowser/visicalc/Asin.java
@@ -8,6 +8,8 @@ public class Asin extends Function
   {
     super (cell, text);
 
+    assert text.startsWith ("@ASIN(") : text;
+
     v = new Expression (parent, cell, functionText).reduce ();
     valueType = ValueType.VALUE;
   }
diff --git a/src/com/bytezone/diskbrowser/visicalc/Atan.java b/src/com/bytezone/diskbrowser/visicalc/Atan.java
index 224ac31..1e36cd7 100644
--- a/src/com/bytezone/diskbrowser/visicalc/Atan.java
+++ b/src/com/bytezone/diskbrowser/visicalc/Atan.java
@@ -8,6 +8,8 @@ public class Atan extends Function
   {
     super (cell, text);
 
+    assert text.startsWith ("@ATAN(") : text;
+
     v = new Expression (parent, cell, functionText).reduce ();
     valueType = ValueType.VALUE;
   }
diff --git a/src/com/bytezone/diskbrowser/visicalc/Average.java b/src/com/bytezone/diskbrowser/visicalc/Average.java
index 745a501..15a4d88 100644
--- a/src/com/bytezone/diskbrowser/visicalc/Average.java
+++ b/src/com/bytezone/diskbrowser/visicalc/Average.java
@@ -11,6 +11,8 @@ public class Average extends Function
   {
     super (cell, text);
 
+    assert text.startsWith ("@AVERAGE(") : text;
+
     list = new ValueList (parent, cell, functionText);
     isRange = functionText.indexOf ("...") > 0;
   }
diff --git a/src/com/bytezone/diskbrowser/visicalc/Choose.java b/src/com/bytezone/diskbrowser/visicalc/Choose.java
index 70f147b..3339ee2 100644
--- a/src/com/bytezone/diskbrowser/visicalc/Choose.java
+++ b/src/com/bytezone/diskbrowser/visicalc/Choose.java
@@ -11,6 +11,8 @@ public class Choose extends Function
   {
     super (cell, text);
 
+    assert text.startsWith ("@CHOOSE(") : text;
+
     //    int pos = functionText.indexOf (',');
     //    sourceText = functionText.substring (0, pos);
     sourceText = Expression.getParameter (functionText);
diff --git a/src/com/bytezone/diskbrowser/visicalc/Cos.java b/src/com/bytezone/diskbrowser/visicalc/Cos.java
index 4accc0e..95a7d08 100644
--- a/src/com/bytezone/diskbrowser/visicalc/Cos.java
+++ b/src/com/bytezone/diskbrowser/visicalc/Cos.java
@@ -8,6 +8,8 @@ public class Cos extends Function
   {
     super (cell, text);
 
+    assert text.startsWith ("@COS(") : text;
+
     v = new Expression (parent, cell, functionText).reduce ();
     valueType = ValueType.VALUE;
   }
diff --git a/src/com/bytezone/diskbrowser/visicalc/Count.java b/src/com/bytezone/diskbrowser/visicalc/Count.java
index 0a81078..68ce695 100644
--- a/src/com/bytezone/diskbrowser/visicalc/Count.java
+++ b/src/com/bytezone/diskbrowser/visicalc/Count.java
@@ -11,6 +11,8 @@ class Count extends Function
   {
     super (cell, text);
 
+    assert text.startsWith ("@COUNT(") : text;
+
     list = new ValueList (parent, cell, functionText);
     isRange = functionText.indexOf ("...") > 0;
   }
diff --git a/src/com/bytezone/diskbrowser/visicalc/Error.java b/src/com/bytezone/diskbrowser/visicalc/Error.java
index 6b9ce61..ed69e6f 100644
--- a/src/com/bytezone/diskbrowser/visicalc/Error.java
+++ b/src/com/bytezone/diskbrowser/visicalc/Error.java
@@ -5,6 +5,9 @@ class Error extends Function
   public Error (Cell cell, String text)
   {
     super (cell, text);
+
+    assert text.startsWith ("@ERROR") : text;
+
     valueType = ValueType.ERROR;
   }
 }
\ No newline at end of file
diff --git a/src/com/bytezone/diskbrowser/visicalc/Exp.java b/src/com/bytezone/diskbrowser/visicalc/Exp.java
index 97e0d9d..fb69594 100644
--- a/src/com/bytezone/diskbrowser/visicalc/Exp.java
+++ b/src/com/bytezone/diskbrowser/visicalc/Exp.java
@@ -8,6 +8,8 @@ public class Exp extends Function
   {
     super (cell, text);
 
+    assert text.startsWith ("@EXP(") : text;
+
     v = new Expression (parent, cell, functionText).reduce ();
     valueType = ValueType.VALUE;
   }
diff --git a/src/com/bytezone/diskbrowser/visicalc/False.java b/src/com/bytezone/diskbrowser/visicalc/False.java
index f4ecea0..30a106a 100644
--- a/src/com/bytezone/diskbrowser/visicalc/False.java
+++ b/src/com/bytezone/diskbrowser/visicalc/False.java
@@ -6,6 +6,8 @@ public class False extends Function
   {
     super (cell, text);
 
+    assert text.equals ("@FALSE") : text;
+
     value = 0;
     valueType = ValueType.VALUE;
   }
diff --git a/src/com/bytezone/diskbrowser/visicalc/If.java b/src/com/bytezone/diskbrowser/visicalc/If.java
index 9b235b9..6a9ba88 100644
--- a/src/com/bytezone/diskbrowser/visicalc/If.java
+++ b/src/com/bytezone/diskbrowser/visicalc/If.java
@@ -14,6 +14,8 @@ class If extends Function
   {
     super (cell, text);
 
+    assert text.startsWith ("@IF(") : text;
+
     conditionText = Expression.getParameter (functionText);
     textTrue =
         Expression.getParameter (functionText.substring (conditionText.length () + 1));
diff --git a/src/com/bytezone/diskbrowser/visicalc/Int.java b/src/com/bytezone/diskbrowser/visicalc/Int.java
index 460c4da..c94f786 100644
--- a/src/com/bytezone/diskbrowser/visicalc/Int.java
+++ b/src/com/bytezone/diskbrowser/visicalc/Int.java
@@ -8,6 +8,8 @@ public class Int extends Function
   {
     super (cell, text);
 
+    assert text.startsWith ("@INT(") : text;
+
     source = new Expression (parent, cell, functionText);
     values.add (source);
   }
diff --git a/src/com/bytezone/diskbrowser/visicalc/IsError.java b/src/com/bytezone/diskbrowser/visicalc/IsError.java
index b577562..7ee87e1 100644
--- a/src/com/bytezone/diskbrowser/visicalc/IsError.java
+++ b/src/com/bytezone/diskbrowser/visicalc/IsError.java
@@ -8,6 +8,8 @@ class IsError extends Function
   {
     super (cell, text);
 
+    assert text.startsWith ("@ISERROR(") : text;
+
     expression = new Expression (parent, cell, functionText).reduce ();
   }
 
diff --git a/src/com/bytezone/diskbrowser/visicalc/IsNa.java b/src/com/bytezone/diskbrowser/visicalc/IsNa.java
index ddf5f99..1b3c09f 100644
--- a/src/com/bytezone/diskbrowser/visicalc/IsNa.java
+++ b/src/com/bytezone/diskbrowser/visicalc/IsNa.java
@@ -8,6 +8,8 @@ public class IsNa extends Function
   {
     super (cell, text);
 
+    assert text.startsWith ("@ISNA(") : text;
+
     expression = new Expression (parent, cell, functionText).reduce ();
   }
 
diff --git a/src/com/bytezone/diskbrowser/visicalc/Ln.java b/src/com/bytezone/diskbrowser/visicalc/Ln.java
index e3e3a50..ce15d6e 100644
--- a/src/com/bytezone/diskbrowser/visicalc/Ln.java
+++ b/src/com/bytezone/diskbrowser/visicalc/Ln.java
@@ -8,6 +8,8 @@ public class Ln extends Function
   {
     super (cell, text);
 
+    assert text.startsWith ("@LN(") : text;
+
     v = new Expression (parent, cell, functionText).reduce ();
     valueType = ValueType.VALUE;
   }
diff --git a/src/com/bytezone/diskbrowser/visicalc/Log10.java b/src/com/bytezone/diskbrowser/visicalc/Log10.java
index 3051e87..6134d01 100644
--- a/src/com/bytezone/diskbrowser/visicalc/Log10.java
+++ b/src/com/bytezone/diskbrowser/visicalc/Log10.java
@@ -8,6 +8,8 @@ public class Log10 extends Function
   {
     super (cell, text);
 
+    assert text.startsWith ("@LOG10(") : text;
+
     v = new Expression (parent, cell, functionText).reduce ();
     valueType = ValueType.VALUE;
   }
diff --git a/src/com/bytezone/diskbrowser/visicalc/Lookup.java b/src/com/bytezone/diskbrowser/visicalc/Lookup.java
index 4f0464e..789cbe3 100644
--- a/src/com/bytezone/diskbrowser/visicalc/Lookup.java
+++ b/src/com/bytezone/diskbrowser/visicalc/Lookup.java
@@ -11,17 +11,14 @@ class Lookup extends Function
   {
     super (cell, text);
 
-    //    int pos = text.indexOf (',');
+    assert text.startsWith ("@LOOKUP(") : text;
+
     sourceText = Expression.getParameter (functionText);
-
-    //    sourceText = text.substring (8, pos);
     source = new Expression (parent, cell, sourceText);
+    values.add (source);
 
-    //    rangeText = text.substring (pos + 1, text.length () - 1);
     rangeText = functionText.substring (sourceText.length () + 1);
     range = new Range (parent, cell, rangeText);
-
-    values.add (source);
   }
 
   @Override
diff --git a/src/com/bytezone/diskbrowser/visicalc/Max.java b/src/com/bytezone/diskbrowser/visicalc/Max.java
index b9caf1b..c5893f9 100644
--- a/src/com/bytezone/diskbrowser/visicalc/Max.java
+++ b/src/com/bytezone/diskbrowser/visicalc/Max.java
@@ -8,6 +8,8 @@ class Max extends Function
   {
     super (cell, text);
 
+    assert text.startsWith ("@MAX(") : text;
+
     list = new ValueList (parent, cell, functionText);
   }
 
diff --git a/src/com/bytezone/diskbrowser/visicalc/Min.java b/src/com/bytezone/diskbrowser/visicalc/Min.java
index 75be45f..f124f29 100644
--- a/src/com/bytezone/diskbrowser/visicalc/Min.java
+++ b/src/com/bytezone/diskbrowser/visicalc/Min.java
@@ -8,6 +8,8 @@ class Min extends Function
   {
     super (cell, text);
 
+    assert text.startsWith ("@MIN(") : text;
+
     list = new ValueList (parent, cell, functionText);
   }
 
diff --git a/src/com/bytezone/diskbrowser/visicalc/Na.java b/src/com/bytezone/diskbrowser/visicalc/Na.java
index f21643c..0fff1a5 100644
--- a/src/com/bytezone/diskbrowser/visicalc/Na.java
+++ b/src/com/bytezone/diskbrowser/visicalc/Na.java
@@ -5,6 +5,9 @@ public class Na extends Function
   public Na (Cell cell, String text)
   {
     super (cell, text);
+
+    assert text.equals ("@NA") : text;
+
     valueType = ValueType.NA;
   }
 }
\ No newline at end of file
diff --git a/src/com/bytezone/diskbrowser/visicalc/Npv.java b/src/com/bytezone/diskbrowser/visicalc/Npv.java
index 0edab39..99e6348 100644
--- a/src/com/bytezone/diskbrowser/visicalc/Npv.java
+++ b/src/com/bytezone/diskbrowser/visicalc/Npv.java
@@ -14,14 +14,14 @@ public class Npv extends Function
   {
     super (cell, text);
 
-    int pos = text.indexOf (',');
-    valueText = text.substring (5, pos);
-    rangeText = text.substring (pos + 1, text.length () - 1);
+    assert text.startsWith ("@NPV(") : text;
 
+    valueText = Expression.getParameter (functionText);
     rateExp = new Expression (parent, cell, valueText);
-    range = new Range (parent, cell, rangeText);
-
     values.add (rateExp);
+
+    rangeText = functionText.substring (valueText.length () + 1);
+    range = new Range (parent, cell, rangeText);
   }
 
   @Override
diff --git a/src/com/bytezone/diskbrowser/visicalc/Or.java b/src/com/bytezone/diskbrowser/visicalc/Or.java
index ff5757b..6ffb616 100644
--- a/src/com/bytezone/diskbrowser/visicalc/Or.java
+++ b/src/com/bytezone/diskbrowser/visicalc/Or.java
@@ -11,14 +11,13 @@ class Or extends Function
   {
     super (cell, text);
 
+    assert text.startsWith ("@OR(") : text;
+
     String remainder = functionText;
     while (true)
     {
       String parameter = Expression.getParameter (remainder);
-      //      System.out.printf ("cond: [%s]%n", parameter);
       conditions.add (new Condition (parent, cell, parameter));
-      //      System.out.printf ("  [%s]%n", remainder);
-      //      System.out.printf ("  [%s]%n", parameter);
       if (remainder.length () == parameter.length ())
         break;
       remainder = remainder.substring (parameter.length () + 1);
diff --git a/src/com/bytezone/diskbrowser/visicalc/Pi.java b/src/com/bytezone/diskbrowser/visicalc/Pi.java
index ecb8e24..d7dcb3d 100644
--- a/src/com/bytezone/diskbrowser/visicalc/Pi.java
+++ b/src/com/bytezone/diskbrowser/visicalc/Pi.java
@@ -7,6 +7,9 @@ class Pi extends Function
     super (cell, text);
 
     value = Math.PI;
+
+    assert text.equals ("@PI") : text;
+
     valueType = ValueType.VALUE;
   }
 }
\ No newline at end of file
diff --git a/src/com/bytezone/diskbrowser/visicalc/Sheet.java b/src/com/bytezone/diskbrowser/visicalc/Sheet.java
index 00e1e4f..8254852 100644
--- a/src/com/bytezone/diskbrowser/visicalc/Sheet.java
+++ b/src/com/bytezone/diskbrowser/visicalc/Sheet.java
@@ -500,129 +500,118 @@ public class Sheet
       return new Error (cell, "@ERROR");
     }
 
+    String functionName = "";
+    int functionId = -1;
     for (int i = 0; i < Function.functionList.length; i++)
       if (text.startsWith (Function.functionList[i]))
       {
+        functionId = i;
         functionTotals[i]++;
+        functionName = Function.functionList[i];
         break;
       }
 
-    if (text.charAt (1) == 'A')
+    if (functionName.isEmpty ())
     {
-      if (text.startsWith ("@ABS("))
+      System.out.printf ("Unknown function: [%s]%n", text);
+      return new Error (cell, "@ERROR");
+    }
+
+    switch (functionId)
+    {
+      case 0:
         return new Abs (cell, text);
 
-      if (text.startsWith ("@ACOS("))
+      case 1:
         return new Acos (cell, text);
 
-      if (text.startsWith ("@AND("))
+      case 2:
         return new And (cell, text);
 
-      if (text.startsWith ("@ASIN("))
+      case 3:
         return new Asin (cell, text);
 
-      if (text.startsWith ("@ATAN("))
+      case 4:
         return new Atan (cell, text);
 
-      if (text.startsWith ("@AVERAGE("))
+      case 5:
         return new Average (cell, text);
-    }
-    else if (text.charAt (1) == 'C')
-    {
-      if (text.startsWith ("@COUNT("))
+
+      case 6:
         return new Count (cell, text);
 
-      if (text.startsWith ("@CHOOSE("))
+      case 7:
         return new Choose (cell, text);
 
-      if (text.startsWith ("@COS("))
+      case 8:
         return new Cos (cell, text);
-    }
-    else if (text.charAt (1) == 'E')
-    {
-      if (text.startsWith ("@ERROR"))
+
+      case 9:
         return new Error (cell, text);
 
-      if (text.startsWith ("@EXP("))
+      case 10:
         return new Exp (cell, text);
-    }
-    else if (text.charAt (1) == 'F')
-    {
-      if (text.startsWith ("@FALSE"))
+
+      case 11:
         return new False (cell, text);
-    }
-    else if (text.charAt (1) == 'I')
-    {
-      if (text.startsWith ("@IF("))
+
+      case 12:
         return new If (cell, text);
 
-      if (text.startsWith ("@INT("))
+      case 13:
         return new Int (cell, text);
 
-      if (text.startsWith ("@ISERROR("))
+      case 14:
         return new IsError (cell, text);
 
-      if (text.startsWith ("@ISNA("))
+      case 15:
         return new IsNa (cell, text);
-    }
-    else if (text.charAt (1) == 'L')
-    {
-      if (text.startsWith ("@LOG10("))
+
+      case 16:
         return new Log10 (cell, text);
 
-      if (text.startsWith ("@LOOKUP("))
+      case 17:
         return new Lookup (cell, text);
 
-      if (text.startsWith ("@LN("))
+      case 18:
         return new Ln (cell, text);
-    }
-    else if (text.charAt (1) == 'M')
-    {
-      if (text.startsWith ("@MIN("))
+
+      case 19:
         return new Min (cell, text);
 
-      if (text.startsWith ("@MAX("))
+      case 20:
         return new Max (cell, text);
-    }
-    else if (text.charAt (1) == 'N')
-    {
-      if (text.equals ("@NA"))
+
+      case 21:
         return new Na (cell, text);
 
-      if (text.startsWith ("@NPV("))
+      case 22:
         return new Npv (cell, text);
-    }
-    else if (text.charAt (1) == 'O')
-    {
-      if (text.startsWith ("@OR("))
+
+      case 23:
         return new Or (cell, text);
-    }
-    else if (text.charAt (1) == 'P')
-    {
-      if (text.startsWith ("@PI"))
+
+      case 24:
         return new Pi (cell, text);
-    }
-    else if (text.charAt (1) == 'S')
-    {
-      if (text.startsWith ("@SIN("))
+
+      case 25:
         return new Sin (cell, text);
 
-      if (text.startsWith ("@SUM("))
+      case 26:
         return new Sum (cell, text);
 
-      if (text.startsWith ("@SQRT("))
+      case 27:
         return new Sqrt (cell, text);
-    }
-    else if (text.charAt (1) == 'T')
-    {
-      if (text.startsWith ("@TAN("))
+
+      case 28:
         return new Tan (cell, text);
 
-      if (text.startsWith ("@TRUE"))
+      case 29:
         return new True (cell, text);
-    }
 
-    System.out.printf ("Unknown function: [%s]%n", text);
-    return new Error (cell, "@ERROR");
+      default:
+        System.out.printf ("Unknown function: [%s]%n", text);
+        return new Error (cell, "@ERROR");
+    }
   }
 }
\ No newline at end of file
diff --git a/src/com/bytezone/diskbrowser/visicalc/Sin.java b/src/com/bytezone/diskbrowser/visicalc/Sin.java
index b760bb7..b01de26 100644
--- a/src/com/bytezone/diskbrowser/visicalc/Sin.java
+++ b/src/com/bytezone/diskbrowser/visicalc/Sin.java
@@ -8,6 +8,8 @@ public class Sin extends Function
   {
     super (cell, text);
 
+    assert text.startsWith ("@SIN(") : text;
+
     v = new Expression (parent, cell, functionText).reduce ();
     valueType = ValueType.VALUE;
   }
diff --git a/src/com/bytezone/diskbrowser/visicalc/Sqrt.java b/src/com/bytezone/diskbrowser/visicalc/Sqrt.java
index dad018e..6819ed1 100644
--- a/src/com/bytezone/diskbrowser/visicalc/Sqrt.java
+++ b/src/com/bytezone/diskbrowser/visicalc/Sqrt.java
@@ -7,7 +7,10 @@ public class Sqrt extends Function
   Sqrt (Cell cell, String text)
   {
     super (cell, text);
-    source = new Expression (parent, cell, text.substring (5, text.length () - 1));
+
+    assert text.startsWith ("@SQRT(") : text;
+
+    source = new Expression (parent, cell, functionText);
     values.add (source);
   }
 
diff --git a/src/com/bytezone/diskbrowser/visicalc/Sum.java b/src/com/bytezone/diskbrowser/visicalc/Sum.java
index 4ebcbab..53cd1af 100644
--- a/src/com/bytezone/diskbrowser/visicalc/Sum.java
+++ b/src/com/bytezone/diskbrowser/visicalc/Sum.java
@@ -8,6 +8,8 @@ class Sum extends Function
   {
     super (cell, text);
 
+    assert text.startsWith ("@SUM(") : text;
+
     list = new ValueList (parent, cell, functionText);
   }
 
diff --git a/src/com/bytezone/diskbrowser/visicalc/Tan.java b/src/com/bytezone/diskbrowser/visicalc/Tan.java
index 7b78f24..4ef515d 100644
--- a/src/com/bytezone/diskbrowser/visicalc/Tan.java
+++ b/src/com/bytezone/diskbrowser/visicalc/Tan.java
@@ -8,6 +8,8 @@ public class Tan extends Function
   {
     super (cell, text);
 
+    assert text.startsWith ("@TAN(") : text;
+
     v = new Expression (parent, cell, functionText).reduce ();
     valueType = ValueType.VALUE;
   }
diff --git a/src/com/bytezone/diskbrowser/visicalc/True.java b/src/com/bytezone/diskbrowser/visicalc/True.java
index 1f1548b..5622c1f 100644
--- a/src/com/bytezone/diskbrowser/visicalc/True.java
+++ b/src/com/bytezone/diskbrowser/visicalc/True.java
@@ -6,6 +6,8 @@ public class True extends Function
   {
     super (cell, text);
 
+    assert text.equals ("@TRUE") : text;
+
     value = 1;
     valueType = ValueType.VALUE;
   }