diff --git a/ClosedXML/ClosedXML/ClosedXML/Excel/DataValidation/IXLDataValidations.cs b/ClosedXML/ClosedXML/ClosedXML/Excel/DataValidation/IXLDataValidations.cs
index a5bc443..424a0f0 100644
--- a/ClosedXML/ClosedXML/ClosedXML/Excel/DataValidation/IXLDataValidations.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/Excel/DataValidation/IXLDataValidations.cs
@@ -8,5 +8,6 @@
     public interface IXLDataValidations: IEnumerable<IXLDataValidation>
     {
         void Add(IXLDataValidation dataValidation);
+        Boolean ContainsSingle(IXLRange range);
     }
 }
diff --git a/ClosedXML/ClosedXML/ClosedXML/Excel/DataValidation/XLDataValidations.cs b/ClosedXML/ClosedXML/ClosedXML/Excel/DataValidation/XLDataValidations.cs
index 05aba35..b20d6f5 100644
--- a/ClosedXML/ClosedXML/ClosedXML/Excel/DataValidation/XLDataValidations.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/Excel/DataValidation/XLDataValidations.cs
@@ -27,5 +27,15 @@
         {
             return GetEnumerator();
         }
+
+        public Boolean ContainsSingle(IXLRange range)
+        {
+            foreach (var dv in dataValidations)
+            {
+                if (dv.Ranges.Count == 1 && dv.Ranges.Contains(range))
+                    return true;
+            }
+            return false;
+        }
     }
 }
diff --git a/ClosedXML/ClosedXML/ClosedXML/Excel/Ranges/IXLRanges.cs b/ClosedXML/ClosedXML/ClosedXML/Excel/Ranges/IXLRanges.cs
index 0506ff6..5e6e5a3 100644
--- a/ClosedXML/ClosedXML/ClosedXML/Excel/Ranges/IXLRanges.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/Excel/Ranges/IXLRanges.cs
@@ -22,6 +22,8 @@
         /// <param name="range">The range to remove from this group.</param>
         void Remove(IXLRange range);
 
+        Int32 Count { get; }
+
         Boolean Contains(IXLRange range);
 
         IXLStyle Style { get; set; }
diff --git a/ClosedXML/ClosedXML/ClosedXML/Excel/Ranges/XLRange.cs b/ClosedXML/ClosedXML/ClosedXML/Excel/Ranges/XLRange.cs
index 996842d..b0b408d 100644
--- a/ClosedXML/ClosedXML/ClosedXML/Excel/Ranges/XLRange.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/Excel/Ranges/XLRange.cs
@@ -969,10 +969,12 @@
             return FindColumns(search, searchContents, false, false);
         }
         public IXLRangeColumns FindColumns(String search, XLSearchContents searchContents, Boolean useRegularExpressions)
-        { 
+        {
+            throw new NotImplementedException();
         }
         public IXLRangeColumns FindColumns(String search, XLSearchContents searchContents, Boolean matchCase, Boolean entireCell)
-        { 
+        {
+            throw new NotImplementedException();
         }
 
         public IXLRangeRows FindRows(String search)
@@ -985,9 +987,11 @@
         }
         public IXLRangeRows FindRows(String search, XLSearchContents searchContents, Boolean useRegularExpressions)
         {
+            throw new NotImplementedException();
         }
         public IXLRangeRows FindRows(String search, XLSearchContents searchContents, Boolean matchCase, Boolean entireCell)
         {
+            throw new NotImplementedException();
         }
 
         public new IXLRange Replace(String oldValue, String newValue)
diff --git a/ClosedXML/ClosedXML/ClosedXML/Excel/Ranges/XLRangeBase.cs b/ClosedXML/ClosedXML/ClosedXML/Excel/Ranges/XLRangeBase.cs
index 6766d38..124539d 100644
--- a/ClosedXML/ClosedXML/ClosedXML/Excel/Ranges/XLRangeBase.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/Excel/Ranges/XLRangeBase.cs
@@ -945,13 +945,10 @@
         {
             get 
             {
-                String address = this.RangeAddress.ToString();
-                if (Worksheet.DataValidations.Where(dv => 
-                    dv.Ranges.Count() == 1
-                    && dv.Ranges.Contains(this.AsRange())
-                    ).Any())
+                var thisRange = this.AsRange();
+                if (Worksheet.DataValidations.ContainsSingle(thisRange))
                 {
-                    return Worksheet.DataValidations.Where(dv => dv.Ranges.Contains(this.AsRange())).Single();
+                    return Worksheet.DataValidations.Where(dv => dv.Ranges.Contains(thisRange)).Single();
                 }
                 else
                 {
@@ -1051,9 +1048,11 @@
         }
         public IXLCells FindCells(String search, XLSearchContents searchContents, Boolean useRegularExpressions)
         {
+            throw new NotImplementedException();
         }
         public IXLCells FindCells(String search, XLSearchContents searchContents, Boolean matchCase, Boolean entireCell)
         {
+            throw new NotImplementedException();
         }
 
         public IXLRangeBase Replace(String oldValue, String newValue)
@@ -1066,7 +1065,7 @@
         }
         public IXLRangeBase Replace(String oldValue, String newValue, XLSearchContents searchContents, Boolean useRegularExpressions)
         {
-            
+            throw new NotImplementedException();
         }
     }
 }
diff --git a/ClosedXML/ClosedXML/ClosedXML/Excel/Ranges/XLRanges.cs b/ClosedXML/ClosedXML/ClosedXML/Excel/Ranges/XLRanges.cs
index fb0c7f3..a5f3d2e 100644
--- a/ClosedXML/ClosedXML/ClosedXML/Excel/Ranges/XLRanges.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/Excel/Ranges/XLRanges.cs
@@ -23,10 +23,12 @@
 
         public void Add(IXLRange range)
         {
+            count++;
             ranges.Add((XLRange)range);
         }
         public void Add(String rangeAddress)
         {
+            count++;
             var byExclamation = rangeAddress.Split('!');
             var wsName = byExclamation[0].Replace("'", "");
             var rng = byExclamation[1];
@@ -35,9 +37,16 @@
         }
         public void Remove(IXLRange range)
         {
+            count--;
             ranges.RemoveAll(r => r.ToString() == range.ToString());
         }
 
+        private Int32 count;
+        public Int32 Count {
+            get { return count; }
+            private set { count = value; }
+        }
+
         public IEnumerator<IXLRange> GetEnumerator()
         {
             var retList = new List<IXLRange>();
diff --git a/ClosedXML/ClosedXML/ClosedXML/Excel/Tables/XLTable.cs b/ClosedXML/ClosedXML/ClosedXML/Excel/Tables/XLTable.cs
index a72b43f..5369185 100644
--- a/ClosedXML/ClosedXML/ClosedXML/Excel/Tables/XLTable.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/Excel/Tables/XLTable.cs
@@ -360,9 +360,11 @@
         }
         public new IXLTableRows FindRows(String search, XLSearchContents searchContents, Boolean useRegularExpressions)
         {
+            throw new NotImplementedException();
         }
         public new IXLTableRows FindRows(String search, XLSearchContents searchContents, Boolean matchCase, Boolean entireCell)
         {
+            throw new NotImplementedException();
         }
 
         public new IXLTable Replace(String oldValue, String newValue)
diff --git a/ClosedXML/ClosedXML/ClosedXML/Excel/XLAddress.cs b/ClosedXML/ClosedXML/ClosedXML/Excel/XLAddress.cs
index bd4e165..1672bea 100644
--- a/ClosedXML/ClosedXML/ClosedXML/Excel/XLAddress.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/Excel/XLAddress.cs
@@ -7,7 +7,7 @@
 
 namespace ClosedXML.Excel
 {
-    internal struct XLAddress: IXLAddress
+    internal class XLAddress: IXLAddress
     {
         #region Constructors
         /// <summary>
diff --git a/ClosedXML/ClosedXML/ClosedXML/Excel/XLWorksheet.cs b/ClosedXML/ClosedXML/ClosedXML/Excel/XLWorksheet.cs
index 49b39e6..e214c44 100644
--- a/ClosedXML/ClosedXML/ClosedXML/Excel/XLWorksheet.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/Excel/XLWorksheet.cs
@@ -821,9 +821,11 @@
         }
         public IXLColumns FindColumns(String search, XLSearchContents searchContents, Boolean useRegularExpressions)
         {
+            throw new NotImplementedException();
         }
         public IXLColumns FindColumns(String search, XLSearchContents searchContents, Boolean matchCase, Boolean entireCell)
         {
+            throw new NotImplementedException();
         }
 
         public IXLRows FindRows(String search)
@@ -836,9 +838,11 @@
         }
         public IXLRows FindRows(String search, XLSearchContents searchContents, Boolean useRegularExpressions)
         {
+            throw new NotImplementedException();
         }
         public IXLRows FindRows(String search, XLSearchContents searchContents, Boolean matchCase, Boolean entireCell)
         {
+            throw new NotImplementedException();
         }
 
         public new IXLWorksheet Replace(String oldValue, String newValue)
diff --git a/ClosedXML/ClosedXML/ClosedXML_Sandbox/Program.cs b/ClosedXML/ClosedXML/ClosedXML_Sandbox/Program.cs
index cface98..efc4cc8 100644
--- a/ClosedXML/ClosedXML/ClosedXML_Sandbox/Program.cs
+++ b/ClosedXML/ClosedXML/ClosedXML_Sandbox/Program.cs
@@ -15,19 +15,20 @@
         static void Main(string[] args)
         {
             //var fileName = "BasicTable";
-            var fileName = "Sandbox";
-            //var fileName = "Issue_6429";
-            //var wb = new XLWorkbook(String.Format(@"c:\Excel Files\ForTesting\{0}.xlsx", fileName));
-            var wb = new XLWorkbook();
-            var ws = wb.Worksheets.Add("Sheet1");
-            ws.Cell("A1").Value = "Category";
-            ws.Cell("A2").Value = "A";
-            ws.Cell("A3").Value = "B";
-            ws.Cell("B1").Value = "Value";
-            ws.Cell("B2").Value = 5;
-            ws.Cell("B3").Value = 10;
+            //var fileName = "Sandbox";
+            var fileName = "Issue_6510";
+            var wb = new XLWorkbook(String.Format(@"c:\Excel Files\ForTesting\{0}.xlsx", fileName));
+            //var wb = new XLWorkbook();
+            //var ws = wb.Worksheets.Add("Sheet1");
+            //ws.Cell("A1").Value = "Category";
+            //ws.Cell("A2").Value = "A";
+            //ws.Cell("A3").Value = "B";
+            //ws.Cell("B1").Value = "Value";
+            //ws.Cell("B2").Value = 5;
+            //ws.Cell("B3").Value = 10;
 
             wb.SaveAs(String.Format(@"c:\Excel Files\ForTesting\{0}_Saved.xlsx", fileName));
+            //Console.ReadKey();
         }
 
 
@@ -59,7 +60,7 @@
                     {
                         foreach (var co in Enumerable.Range(1, 5))
                         {
-                            //ws.Cell(ro, co).Style = GetRandomStyle();
+                            ws.Cell(ro, co).Style = GetRandomStyle();
                             //if (rnd.Next(1, 5) == 1)
                                 //ws.Cell(ro, co).FormulaA1 = ws.Cell(ro + 1, co + 1).Address.ToString() + " & \"-Copy\"";
                             //else
@@ -67,6 +68,13 @@
                         }
                         //System.Threading.Thread.Sleep(10);
                     }
+                    
+                    Int32 rowCount = ws.LastRowUsed().RowNumber();
+                    for (Int32 ro = 1; ro <= rowCount; ro += 100)
+                    {
+                        var dv = ws.Range(ro, 1, ro + 99, 5).DataValidation;
+                    }
+
                     //ws.RangeUsed().Style.Border.BottomBorder = XLBorderStyleValues.DashDot;
                     //ws.RangeUsed().Style.Border.BottomBorderColor = XLColor.AirForceBlue;
                     //ws.RangeUsed().Style.Border.TopBorder = XLBorderStyleValues.DashDotDot;
@@ -85,12 +93,12 @@
                     //ws.RangeUsed().Style.Alignment.Vertical = XLAlignmentVerticalValues.Center;
                     //ws.RangeUsed().Style.Alignment.WrapText = true;
 
-                    var startS = DateTime.Now;
-                    ws.Sort();
-                    var endS = DateTime.Now;
-                    var savedS = (endS - startS).TotalSeconds;
-                    runningSave.Add(savedS);
-                    Console.WriteLine("Sorted in {0} secs.", savedS);
+                    //var startS = DateTime.Now;
+                    //ws.Sort();
+                    //var endS = DateTime.Now;
+                    //var savedS = (endS - startS).TotalSeconds;
+                    //runningSave.Add(savedS);
+                    //Console.WriteLine("Sorted in {0} secs.", savedS);
                 }
 
 
@@ -103,7 +111,7 @@
                 //Console.WriteLine("Bolded all cells in {0} secs.", (end3 - start3).TotalSeconds);
                 
                 var start = DateTime.Now;
-                //wb.SaveAs(@"C:\Excel Files\ForTesting\Benchmark.xlsx");
+                wb.SaveAs(@"C:\Excel Files\ForTesting\Benchmark.xlsx");
                 var end = DateTime.Now;
                 var saved = (end - start).TotalSeconds;
                 runningSave.Add(saved);
@@ -130,7 +138,7 @@
             Console.WriteLine("Avg Save time: {0}", runningSave.Average());
             Console.WriteLine("Avg Load time: {0}", runningLoad.Average());
             Console.WriteLine("Avg Save Back time: {0}", runningSavedBack.Average());
-            Console.ReadKey();
+            //Console.ReadKey();
         }
 
         private static IXLStyle style1;