Father was an obsessive and even a meticulous notes- and records-keeper. Maybe he realized over the years that a written record of all kind of things - repairs, medical treatments, bills, negotiations, household expenses etc (the range is vast) - is invaluable. So he filled diaries big and small with his jottings and records. He also organized all manner of paperwork into files whose covers - inside and outside - were replete with wall-to-wall notations, as it were.
The locus classicus of his meticulous recordkeeping was this white "address board", which was crammed with all manner of contacts; another example of his 'address card' is also appended.
Here are some other examples - notebooks which contain records of mom's health (sugar levels etc), addresses, life-event notes...