EXCEL/VBA - Write a record log into a sheet, appending at its bottom end

Public Function setLog( _

    SessionID As String _

    , functionName As String _

    , sql As String _

    , Optional userName As String _

) As Boolean

    ' Validate

    'Dim iris As New cIRIS

    If Not getSheetExistance("Log") Then

        setLog = False

        Exit Function

    End If

    ' Target Row

    Dim targetRow As Long

    targetRow = Cells(Rows.Count, 1).End(xlUp).Row + 1

    ' Log

    ThisWorkbook.Sheets("Log").Range("A1").Select

    Range("A" & CStr(targetRow)).Value = SessionID

    Range("B" & CStr(targetRow)).Value = Now()

    Range("C" & CStr(targetRow)).Value = sql

    Range("D" & CStr(targetRow)).Value = functionName

    Range("E" & CStr(targetRow)).Value = userName

    Range("F" & CStr(targetRow)).Formula = "=(B" & targetRow & "-B" & (targetRow - 1) & ")/0.0000115740741118013"

   

End Function