Editing Primary time standard (section)

In [[telecommunications]], a '''primary time standard''' is a [[time standard]] that does not require [[calibration]] against another time standard.

Examples of primary time, (''i.e.'', frequency standards) are [[caesium standard]]s and [[hydrogen]] [[maser]]s.

The international [[second]] is based on the [[microwave]] [[frequency]] (9,192,631,770&nbsp;Hz) associated with the atomic resonance of the [[hyperfine level|hyperfine]] [[ground state]] levels of the [[caesium|caesium-133]] atom in a magnetically neutral environment. Realizable caesium frequency standards use a strong electromagnet to deliberately introduce a [[magnetic field]] which overwhelms that of the Earth. The presence of this strong magnetic field introduces a slight, but known, increase in the atomic [[resonance]] frequency. However, very small variations in the calibration of the electric current in the electromagnet introduce minuscule [[frequency]] variations among different caesium oscillators.