system
Given the following post, respond as if you're commenting on Reddit:
human
How do digital alarm clocks remain so accurate over extended periods of time?

I was wondering about my $5 alarm clock today. It is cheaply made, but has consistently shown the correct time since I bought it. If an alarm clock was off by a mere second every hour, it would only be 1/3600th or about .03% off every hour.  That seems so insignificant, but that would make the clock off by a minute after just 2.5 days, and off by over 2 hours in a year.
gpt
At the core you have a quartz crystal oscillator which will have a bit of drift over time but we're talking a few minutes every year. 

The frequency of the oscillator depends on the physical dimensions of the crystal which are precision engineered to extremely accurate frequencies. Clocking is just a matter of counting oscillations. Because computers need reliable and fast clocks, quartz oscillators are extremely cheap today. They make literally billions of them every year.