Clock making changed dramatically with the invention of the quartz movement over 4 decades ago. Before that, battery operated movements were not as reliable, and some models actually had to be properly balanced just to operate.
Now, quartz movements use a slice of a cultured quartz crystal bar, which is very accurately angle cut, and when electrified, resonates, causing the electrical circuit around it to produce a specific frequency output. Imagine a tuning fork that can run essentially forever (or at least until you need to change the batteries). , The accuracy and stability of quartz crystals is nothing short of amazing. This makes it easy to have clock movements that are accurate to within a couple of minutes a year.