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