You don’t change the setting on your metronome. You just mentally subdivide the time between clicks differently. Griff does the entire course at 60 BPM.
One note per click=quarter notes. 1-2-3-4.
Two notes per click=eighth notes. 1 and 2 and 3 and 4 and
Four notes per click=16th notes. 1 e and a 2 e and a, etc.
Three notes per click = triplets 1 and a 2 and a 3 and a.
Things get faster as you go along because you play more notes per beat, not because you increase the tempo.
If you reset your metronome to higher tempos and still play one note per click, your counting doesn’t change. You are just playing the same thing as faster speeds. Griff could just give us an exercise and say “OK, now just play it faster and faster”. He would only have to print it once.
But each exercise is written out 3 times. The notes are the same. The tempo stays the same. But the subdivisions of the beat get smaller, leading to more notes per measure, which you actually have to play faster.
Again, if you change your metronome to faster tempos and play one note per click, you are not playing different note values. You are just playing the same thing at faster speed. You are not counting subdivisions within beats.
You don’t have to be with Griff very long to realize he’s adamant about owning the beat and being able to count. That’s why he stresses timing at the very beginning of this course and never changes the tempo throughout all the exercises. It’s the counting that changes, not the tempo.
Think about this. What would you do when you encounter quarter, 8th and 16th notes in the same passage? You can’t reset your metronome each time you encounter a different value note. Time marches on. The tempo doesn’t change. You have to be able to mentally subdivide the beat and change your counting to accommodate the different notes.
If you need to actually hear something on the subdivision of a beat, you can find metronomes that actually play subdivisions. For example, it might play a loud click on 1, and different sounds on the subdivisions. Or provide drum tracks that do the same. But you still would keep the tempo the same from one exercise to the next. The notes would just fall on different subdivisions