Binary Search Algorithm

Apparently, only 10 percent of programmers can correctly code the binary search algorithm. What follows is my attempt to prove once and for all that I belong to that select group of programmers! I implemented the algorithm in Excel VBA.

Option Explicit
'++++++++++++++++++++++++++++++++++++++++++++++++
' Author: Ram Limbu
' Date: 2010/04/28
' Description: Binary Search Algorithm in VBA
'++++++++++++++++++++++++++++++++++++++++++++++++

Sub BinaySearch()
    Dim UpperLimit As Long
    Dim LowerLimit As Long
    Dim Mid As Long
    Dim Val As Long
    Dim NotFound As Boolean
    Dim WS As Worksheet

    On Error GoTo ErrRtn

    'prompt user to enter the number to search
    Val = InputBox("Please, enter the number to search")

    'set WS to the first Worksheet
    Set WS = ThisWorkbook.Worksheets(1)

    NotFound = True
    LowerLimit = 1

    UpperLimit = WS.Cells(65536, 1).End(xlUp).Row

    If UpperLimit = 1 And IsEmpty(WS.Cells(1, 1).Value) Then
        MsgBox "The Column A on Worksheet1 is empty. Exiting ..."
        Exit Sub
    End If

    While NotFound And LowerLimit <= UpperLimit
        Mid = (LowerLimit + UpperLimit) \ 2 ' perform integer division     
        If Val = WS.Cells(Mid, 1) Then
            NotFound = False
        ElseIf Val < WS.Cells(Mid, 1) Then
            UpperLimit = Mid - 1
        Else
            LowerLimit = Mid + 1
        End If
    Wend

    If NotFound Then
        MsgBox Val & " wasn't found"
    Else
        WS.Cells(Mid, 1).Select
        MsgBox Val & " was found at row " & Mid
    End If
    Exit Sub
ErrRtn:
    MsgBox Err.Description
End Sub

The assumptions are as follows: (1) The data set is pre-ordered and (2) located on Column A of the first Worksheet. To keep the code simple, no data validation is performed.