This is my lecture on BPM and metronome calculation (e.g., crotchet/quarter note=100, quaver/eighth note=180 etc.), metronome changes in performance practice, and Metric Modulation. (with examples from the music of Elliott Carter)
After following the course, I hope you will be able to understand the physical/acoustic meaning of the metronome, and practice/perform when there is a change of metronome, either with or without a pivot rhythmic unit. I suggest to check Bartok's The Miraculous Mandarin or any music by Magnus Lindberg if you want to apply the knowledge and practice that you learned from this lecture.