Ok, step 1, look at waveform and FFT to determine the accuracy of the peaks.

Finally seeing the waveform of 'Sample' from column B, the repeating pattern demands that the higher frequencies always repeat in the same area of the main 52hz indefinitely.

To check this, we starting with peak #1 and peak #2.

Peak #1 is strongest at 52.7hz, but, just a little slower as you see in my illustration, however, for now, we will call this 52.7hz.

Peak #2 is strongest at 246.1hz, but looking at the strength of the points to the left and right, we can see it should be a little higher.

Now for some math. Take 246.1 and divide by 52.7 and you get approximately 4.7. Now, we know this is too close to 5 to be a coincidence, so we do the reverse and take 52.7 x 5 = 263.5hz. A little too high.

Lets also check peak 3 at 351.6hz / 52.7 = 6.7. This is also to close to 7 and also lets see the opposite. 52.7*7=368.9hz, also a little too high.

Now if you are aware that the lower the frequency, the less accurate the Fourier hz measurement since it sees fewer sine oscillation over your 1024 samples compared to your higher frequency readings. If you understand this, this next step will make sense. If you don't, I'll show you another way to get a more accurate value on that 52.7hz...

Ok, refine the 3 frequencies, take them high ones and divide them down to 52.7hz.

peak3 = 351.6/7 = 50.2

peak2 = 246.1/5 = 49.2

peak1 = 52.7 = 52.7

take the average 50.2+49.2+52.7 = 152.1 / 3 = 50.7hz. (I know this is still a little off, but, it will do for now)

This time if you redo the above 2 steps at the beginning, the number have gotten really close.

peak2 246.1hz/50.7hz=4.85. (looking at the Fourier chart, we know point #2 should be a little higher than 246.1, this will even out)

peak3 = 351.6hz/50.7hz=6.93 (Again, looking at the Fourier chart, we know point #3 should be only a pinch higher than 351.6, this will even out)

These 2 numbers peaks have gotten really close to 5x and 7x. In fact now, if we multiply the base 50.7hz*5, we get 253.5hz and judging by the chart, this looks like it's the exact right value. Same with 50.7hz*7 = 354.9hz, judging on the chart, this also looks perfect.

Next post, making a superior Excel spread sheet which allows you to play with these figures. Give me 30 minutes...