Jitter can be measured in either the time domain or the frequency domain. In the time domain period jitter, cycle-to-cycle jitter, or Time Interval Error can be measured.  In the timing diagram at the top of the slide a signal without jitter is shown, below that a signal with jitter, where the edges are not necessarily located at their ideal position. In the frequency domain the power spectral density of the frequency or phase inaccuracy can be measured. Frequency domain jitter is always measured on one side of the carrier frequency, that is, the right hand or  positive side. Phase noise is measured in –dBc per Hertz at various offsets from the carrier frequency. RMS phase jitter is equal to the integral of the area under the positive curve of the phase noise jitter. An integration range must be specified, a wider range typically implies a higher RMS phase jitter number.