   end
 
   @doc """
-  Subtract `naive_datetime_2` from `naive_datetime_1`.
-
-  The answer can be returned in any `unit` available from `System.time_unit`.
+  Subtract `naive_datetime2` from `naive_datetime1`.
+
+  The answer can be returned in any `unit` available from `t:System.time_unit/0`.
 
   ## Examples
 

      63579428950
  """
  @spec diff(NaiveDateTime.t, NaiveDateTime.t, System.time_unit) :: integer
  def diff(%NaiveDateTime{} = naive_datetime_1,
           %NaiveDateTime{} = naive_datetime_2,
           unit \\ :second) do
    ndt1_microsecond = to_microsecond(naive_datetime_1)
    ndt2_microsecond = to_microsecond(naive_datetime_2)
    difference = ndt1_microsecond - ndt2_microsecond
    System.convert_time_unit(difference, :microsecond, unit)
  end

  @doc """
  Adds a specified amount of time to a `NaiveDateTime`.

  Accepts an `integer` in any `unit` available from `t:System.time_unit/0`.
  Negative values will be move backwards in time.

  ## Examples
