Why not the long-lasting 15

[bhtooefr]

To expand on that... arguably, HP got even more market lock-in for the 12C in the accounting market back in the day, than TI has gotten for the 81/82/83/83+/84+ family in the educational market.

After all, while textbooks may include button sequences to get the right answer out of a TI calculator, I don't think there's any legal documents that quote the 83+ or 84+ owner's manual as the way that a value was derived...