The greatest HP breakthrough Scientific calcs

[Dave Britten]

My take on it:

35: First pocket scientific calculator
65: First pocket programmable calculator
25: Pocket programmable calculator in a price range accessible to students (~$200)
41: First alphanumeric and expandable programmable calculator from HP
11C: Breakthroughs in size, durability, and power consumption
15C: Huge advance in matrix and complex number handling
28C: First calculator with symbolic algebra

I don't know that I would call the Pioneer line particularly groundbreaking, as LCD calculators of that size were quite common by then, but they were all extremely good.

And if we consider the financial models, I would say the 80, 38E/C, and 12C are of the greatest significance, with an honorable mention to the excellent solver used in the 17B, 27S, 18C, etc.