I have one of the new HP 15c's they created 6-7 years ago. It is the exact same as my dad's from ~1985, but much faster due to the new chip. As great as it is, the Voyage-200 (TI-89 with more RAM, more buttons..etc) would run circles around it for usability. A HP might be able to get the answer first, but with my Voyage the full equation was pretty-printed on the screen and i could adjust each variable without retyping everything.