Calculations of the perturbations

This graph shows the ISS and LAGEOS-2 orbital inclination (in the TEME reference frame).
As already explained here, the orbital inclination varies during one orbit. The amplitude of the ISS sinusoid is 0.04 deg and that of the LAGEOS-2 is 0.0124 deg.

Now suppose that we are not interested in the inclination and that we are only interested in the perturbations of the inclination.
By means of the discrete Fourier transform (DFT), we can calculate the sinusoidal components of the perturbations. Basically, we sample a sufficient number of points of the inclination for, say, 10 orbits, then we elaborate those points with the DFT to obtain many sinusoidal components that reproduce the original inclination, but while the usual graphs show the time in the horizontal axis and the inclination in the vertical axis, the graphs obtained from the DFT show the period of the perturbations (how often the perturbation occurs) in the horizontal axis and several peaks that represent the amplitude of the perturbations in the vertical axis, see next graph.
Here is an example of a typical perturbation graph (this is for the ISS inclination).

X-axis: the DFT outputs the values in the frequency domain (see here for a useful animation), but in this analysis, it's much more useful to show the period of the perturbation as a fraction of the orbital period, so that "1" represents the orbital period (about 92.7 minutes) and 0.5 is half the orbital period.

Y-axis magnitude: the left vertical axis shows the amplitude of the perturbations; the unit of measurement is the same as that used for the transformed values (degrees, in this case).

Y-axis phase: the right vertical axis (the only with a linear scale) shows the "starting point" of the perturbation and it is useful to reconstruct the original element (the inclination, in this case) from a series of sinusoids.

We see that the largest perturbation acting on the ISS inclination is 0.02 deg and it occurs twice in one orbit.
If we look at the previous graph, we see an amplitude which is exactly twice that value because 0.02 deg are above the mean inclination and 0.02 deg are below the mean inclination (the period of this perturbation is half the orbital period).
We also see two much smaller perturbations (totally hidden in the previous graph). The bigger one occurs once in an orbit, while the period of the smaller one is exactly 1/3 of the orbital period.

The number of samples collected to create the graphs in this site is typically in the range 130000 to 150000 and without a specially crafted library, the time taken to transform so many numbers would be prohibitive; thanks to the FFTW library, the whole process takes less than 1 second.
Here is another kind of graph that shows the short-periodic perturbation acceleration of the ISS orbital inclination.

The formulas used to calculate that acceleration is taken from the paper NASA TT F-391 (pdf, 18.2 MiB), page 202 of the pdf file.

The perturbing acceleration of the inclination and of the longitude of the ascending node is only in the cross track direction (orbit normal). This acceleration reaches its maximum when the absolute value of the satellite declination is maximum, while the acceleration is null when the satellite crosses the equator.

The graphs that show the precession of the ascending node are in very good agreement with the values obtained with the formula explained here.