Definition
The regression of the lunar nodes causes the Moon's maximum declination to vary between roughly 18.3 and 28.6 degrees over 18.61 years. This modulates constituent amplitudes by a few per cent, increasing M2 slightly when declination range is small and strengthening the diurnal constituents when it is large. Prediction software applies nodal factors f and u to each constituent for the year concerned, which is why very old tide tables degrade.
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