# File lib/xsd/datatypes.rb, line 551
  def of2tz(offset)
    diffmin = offset * 24 * 60
    if diffmin.zero?
      'Z'
    else
      ((diffmin < 0) ? '-' : '+') << format('%02d:%02d',
        (diffmin.abs / 60.0).to_i, (diffmin.abs % 60.0).to_i)
    end
  end