Thanks, I didn't know about Schlag den Henssler, maybe the idea has been around longer than I thought. And I agree about it feeling a little clinical, that's actually something I've been thinking about because I don't want to lose the minimalist feel in the process, but it certainly needs more "gamification".

I really like the idea of thirds as well. or maybe require different percentages, not only 50% or 33%, can be random to add more into difficulty.

Thanks a lot