There are multiple methods to measure time. In the past, we had unreliable time measuring tools like sundials and hourglasses. Then Christiaan Huygens using the concept of SHM invented the pendulum clock which was the first precise enough time measuring device. Eventually Pendulum was replaced by Quartz Crystals which are used in Analogue clocks and watches. I want to know which method do digital clocks and watches use? It is Quartz crystals or something other? Is that other more precise than Quartz crystal?
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1. Plain old quartz crystals are still widely used.
2. Temperature calibrated quartz crystals. These are chips that has a temperature sensor and a correction table in internal memory for each temperature value. They are calibrated at the factory. They are an order of magnitude more accurate than plain quartz crystals.
3. Power grid frequency. In Western countries power grid frequency is adjusted to be within 10-15 seconds of the true time. The frequency is occasionally increased or decreased when needed.
4. Radio signal. In many areas accurate time marks are broadcast digitally. A chip that decodes the signal costs $1-$2.
5. A time server over Internet.
6. A GPS receiver is pretty affordable these days.
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