Why not just make a z80 math program instead?
I actually hardly used a z80 calc to do my math. My trusty Ti-89 does the trick. It's by the way,an amazing math-calc.

I guess I won't buy the book, since I use my Ti-89, which I just noted. But I do wish you good luck making it, and hope it helps a lot of people.
Oh yeah, hopefully it'll make you rich as well.

I do like math a lot actually. So if you'd just make a general math book one day, perhaps I would be tempted.
Anyway, good luck. Looks nice!