  Solar p-mode frequencies vary with solar activity. It is important to take
this into account when comparing the frequencies observed from epochs that span
different regions of the solar cycle. We present details of how to correct
observed p-mode frequencies for the effects of the solar cycle. We describe
three types of correction. The first allows mode frequencies to be corrected to
a nominal activity level, such as the canonical quiet-Sun level. The second
accounts for the effect on the observed mode frequencies, powers, and damping
rates of the continually varying solar cycle and is pertinent to frequencies
obtained from very long data sets. The third corrects for Sun-as-a-star
observations not seeing all components of the modes. Suitable combinations of
the three correction procedures allow the frequencies obtained from different
sets of data to be compared and enable activity-independent inversions of the
solar interior. As an example of how to apply the corrections we describe those
used to produce a set of definitive Sun-as-a-star frequencies.
