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Surface mount and wire-ended crystals.

Quartz crystals are usually easy to spot as they come in a silvery metal can. In the case of quartz clocks they are usually cylindrical and quite small. Often, you will see two small capacitors adjacent to a crystal, which are required to allow it to vibrate freely. Occasionally, one of these might be a variable capacitor allowing a fine tuning of its resonant frequency, already accurate to around 10 parts per million.