This code relies on the recipient and sender having the same book - not just the same title, but also the same edition or reprint. This means the two books are identical in every way.
The sender writes his plaintext, then randomly opens his book and looks for the first letter of the plaintext anywhere on the page. He then writes the page number, line number, word number, and letter position as the first entry in the cipher. He then opens another random page and finds the second letter of the message and encodes it as page number, line number, word number and letter number. This is repeated until the entire message has been encrypted.
In the book "Haynes Explains Pensioners", ISBN 9781785211058, December 2017 reprint:
H Page 8 Line 10 Word 4 Letter 2 E Page 22 Line 4 Word 8 Letter 2 L Page 6 Line 3 Word 3 Letter 5 L Page 25 Line 2 Word 2 Letter 3 O Page 33 Line 1 Word 2 Letter 1
or
8-10-4-2 22-4-8-2 6-3-3-5 25-2-2-3 33-1-2-1
This is a more secure cipher since without the book it is impossible to identify which letter is being referenced, making frequency analysis impossible.