# File lib/spreadsheet/excel/writer/n_worksheet.rb, line 45
  def encode_date date
    return date if date.is_a? Numeric
    if date.is_a? Time
      date = DateTime.new date.year, date.month, date.day,
                          date.hour, date.min, date.sec
    end
    base = @workbook.date_base
    value = date - base
    if LEAP_ERROR > base
      value += 1
    end
    value
  end