Time and Frequency from A to Z:  X to Z

An acronym for a quartz crystal oscillator.  It usually refers to the simplest types of quartz oscillators that have no compensation for the effects of temperature.

The condition reached during a measurement or calibration when the beat frequency between two input signals is no longer detectable.  Zero beat is often associated with audio frequency calibrations (such as the tuning of musical instruments), when the person performing the measurement can no longer hear the beat frequency or beat note.

A term sometimes used in the military and in navigation as a synonym for Coordinated Universal Time (UTC).  In military shorthand, the letter Z follows a time expressed in UTC.  Zulu is not an official time scale.  The term originated because the word zulu is the radio transmission articulation for the letter Z, and the time zone located on the prime meridian is designated on many time zone maps by the letter Z .