Come now, Sgt: Logbooks aren't for the purposes of reminiscing.
Logbooks are for the purposes protecting one's self from prosecution.
Make sure your Granddad doesn't give his logbook away or make any alterations to the entries in it - 50 Penalty Unit Strict Liability offence times two:
61.355 Retention of personal logbooks
(1) A person commits an offence if:
(a) the person is required to keep a personal logbook under regulation 61.345 or 61.350; and
(b) the person does not retain the logbook for 7 years after the day the last entry is made in it.
Penalty: 50 penalty units.
(2) A person commits an offence if:
(a) the person is required to keep a personal logbook under regulation 61.345 or 61.350; and
(b) the person does not ensure that each entry in the logbook is retained unaltered throughout the period mentioned in subregulation (1).
Penalty: 50 penalty units.
(3) An offence against this regulation is an offence of strict liability.