You want to make sure you get a high-accuracy crystal, but even then you may need to adjust the value of C1 and C2 to keep time accurately. The 32.768kHz crystal is the main timekeeping device for the clock. One button sets NET Degrees, the other sets NET Minutes. In addition to the displays, there are two buttons multiplexed into the display outputs for the clock setting functions. The displays are driven by 2N3904 transistors, since the PIC I/O ports can't sink enough current for 7 LEDs. You can look up this scheme on the internet, but the basic idea is that only one display is on at any given time but our eye perceives all displays to be on simultaneously due to persistence of vision. Just like any digital clock, the microcontroller uses time-division multiplexing to control five 7-segment displays from only 12 I/O pins. The schematic diagram (see picture) and electronic assembly are fairly straightforward since most of the "magic" happens in the microcontroller code.
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