It makes more sense when you use tau as tau is a full rotation, not half rotation. e^tau=1. Also I think that i is not interesting because i * i=-1, but becaus

It makes more sense when you use tau as tau is a full rotation, not half rotation. e^tau=1. Also I think that i is not interesting because i * i=-1, but because i * conjugate(i)=1. I never saw the -1 in the context of complex numbers but if you say it's 1, it's easy to see the unit circle. Similarly, with split-complex numbers, you have j * conjugate(j)=-1. Split complex numbers are about mirror reflection so the -1 makes sense.