Purchase advice questions

[Ron Ross]

You might want to visit the classified section "NOW actually". If you ever get the chance to buy an Hp 42s, it was the best pocket calculator ever available for high end number crunching. Not expandable as was the Hp 41c series, but has a lot more math functions built in. Even a full blown Hp 41cx will come up short as a number crunching tool (However, the hp 41c is much more versatile as IT DOES HAVE real I/O).
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But normally the Hp 42s isn't as readily available, and for general calculator use, the Hp 32sii is often preferred (easier to read screen, simpler to program, has an algebraic solver, nifty fraction mode, just a simpler calculator to use).