Funny you guys mention that! I am still working on a rather challenging piece (Classy Rag). I have been doing exactly what Pallas said: when I felt I had all the notes pat, I set the metronome to 50 and still made some errors, so I set it back to 40 played it even more ridiculously slowly. After a few times it felt like I was a slug going backwards, it became too easy, so I set it to 50 which suddenly wasn't such a challenge any longer.
I'm still working on it, I'm at 70 now it's going okay (most of the time), but 80 is still a struggle. I want to get it up to 100 eventually - I know it's going to be a challenge but sometimes we just gotta push a little harder 🙂
It's probably possible to do all that without a metronome, but personally I notice that when I try to play too slow deliberately, I unconsciously speed up gradually which is quite horrible when I listen back to a recording! So although I agree it wouldn't suit everyone (and you do have impeccable timing, Nightowl), I wholeheartedly recommend trying it!
All that said, I LOVE the Black Forest Polka... one of my favourite pieces to practise 🙂
