The electrical signals can then be sent, recorded, or amplified and turned back into sound by a speaker. The piezoelectrical effect can be reversed so that when an electrical charge is applied to the crystal it will warp as if it were under pressure. By cutting the crystal precisely and applying the right charge, it can be made to vibrate at a constant speed. This causes the electricity to also pulse at the same frequency. The resulting device is called an oscillator and is used in a wide variety of applications including TV and radio transmitters and receivers.
Quartz crystals can also provide oscillations that can be used to drive clocks.
The first quartz crystal clock was built in 1928, and many of today's cheap digital watches use quartz crystal oscillators. A quartz crystal clock will not vary more than a thousandth of a second per day. The study of crystals is crystallography and the scientist who makes the study is a crystallographer. One material that is commonly mistaken for crystal is glass. While glass is very similar in composition to quartz, it has no fixed geometrical arrangement of its atoms and molecules.