Unhook a Raspberry Pi from the mains and it forgets the time and date. It’ll only get them back again if you re-connect it to the Internet or enter the data manually. As a Pi user who doesn’t keep his kit connected – I usually wire and power it up when I need it – and doesn’t always bother with the Ethernet cable when he does, I’ve been after a decent real-time clock (RTC) add-on for quite a while. An RTC allows your Pi to keep time, even when the Pi’s power is cut.
There is no shortage of clip-on boards designed for the Raspberry Pi, almost all designed to make the tiny computer’s GPIO pins more accessible in order to ease the connection of devices to it, particularly ones that operate at voltages that are not Pi friendly.
I came across Pi-Supply’s Pi-Crust add-on board quite by chance, but it immediately caught my eye as quite possibly the most useful add-on for the Raspberry Pi there is. Having ordered one, received it and soldered all the parts together, I’m no longer sure that it is.