Given a value for either phase or 𝚫t, the solver returns the missing value for the specified frequency or period. Note that either the period or the frequency must be specified. If over specified (phase and 𝚫t are given), the phase is used. If both the period and frequency are specified, the frequency is used.

The phase relationship between any two periodic waveforms can be measured as long as they are the same frequency. If they are not the same frequency, the time relationship between them constantly changes. When measuring the phase, it is normally done by picking a feature common between them, for instance their peak value or zero crossing point with increasing amplitude, and measuring 𝚫t.

The following figure depicts the meaning associated with the terms. For any two waveforms of the same frequency, the phase is a measure of the amount of separation in time between them. Given that one period of a sine wave can be thought of as 360°, it is possible to express the separation in time between two waveforms in units of degrees. This is more convenient than expressing the value in seconds because, as the frequency changes the number of seconds per waveform period changes. When phase is expressed in degrees, the phase, or relative spacing between waveforms is unaffected by a change of frequency.

The formulas used to convert between the values are:

When describing a phase relationship, the terms leading and lagging are used. In the figure above, the green waveform appears before the blue one. If we assume the the phase angle is 90°, you would describe the green waveform as leading the blue waveform by 90° or you could say that the blue waveform lags the green one by 90°.