       63579428950
   """
   @spec diff(NaiveDateTime.t, NaiveDateTime.t, System.time_unit) :: integer
-  def diff(%NaiveDateTime{} = naive_datetime_1,
-           %NaiveDateTime{} = naive_datetime_2,
+  def diff(%NaiveDateTime{} = naive_datetime1,
+           %NaiveDateTime{} = naive_datetime2,
            unit \\ :second) do
-    ndt1_microsecond = to_microsecond(naive_datetime_1)
-    ndt2_microsecond = to_microsecond(naive_datetime_2)
+    ndt1_microsecond = to_microsecond(naive_datetime1)
+    ndt2_microsecond = to_microsecond(naive_datetime2)
     difference = ndt1_microsecond - ndt2_microsecond
     System.convert_time_unit(difference, :microsecond, unit)
   end

  end

  @doc """
  Subtract `naive_datetime_2` from `naive_datetime_1`.

  The answer can be returned in any `unit` available from `System.time_unit`.

  ## Examples


  @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
