Short life asset election Example 3

Hello Tutor Ref to F6 chapter 5 pages 35 / 36 section 7.2 & example 3 (short life asset election) And the video. This example is skipped stating it will be covered in Corporation Tax. I have searched however I cannot find any reference in the corporation tax or elsewhere that Covers this example. Looking at the answer sheet, other than introducing the column for a short life asset Its treatment appears no different Can you Please advise me of the correct chapter & section that covers this example (or Is there a section missing from my download ?) Regards Wayneg