Casio SF-4300
I picked up this Casio SF-4300 Digital Diary that was wedged between open stacks of index cards and file folders at the local second-hand store.
After replacing the batteries (3 x CR2032), the unit powered on reading "DATA ERROR, CONSULT THE OWNER'S MANUAL". A quick scan told me to reset the unit using the recessed button on the back, similar to a Playstation controller or calculator.
It's a nifty little PDA. With 32kB of memory, it can save a directory of telephone numbers, memos, a daily schedule, calendar appointments, track home and world times, ping reminders, and do arithmetic. It's important to be mindful of the length of pieces of text, as it can quickly lead to an "OVERFLOW", which requires another reset.
There is also a "SECRET" memory location where one can store information that requires a user password. Perfect for keeping your digital diary away from prying eyes. The only (glaring) omission from its feature set is an address book.
The design suits its 1997 production date very well, and the colours remind me of the Casio F-91W from 1989.
It sits in my desk drawer, and I've been entering in short memos every now and then. Hopefully, it will be a fun look back in a year or two.