If you find this interesting, another cool (and also badly named - "resonance" would actually make some sense for that one!) measurement technique for even tini

If you find this interesting, another cool (and also badly named - "resonance" would actually make some sense for that one!) measurement technique for even tinier signals is lock-in amplification. The idea isn't very complicated, but the Wikipedia explanation is god-awful. I'll try: You modulate the cause of the signal you want to measure with some sine function of frequency f. Then you take the resulting signal and multiply it with the clean sine function of frequency f. You integrate (sum up) the result of that over a long time. Incredible sensitivity (and very slow reaction to changes) results. If you know what a convolution is, the explanation can be shorter.