I have several slide rules, but I use them rarely, and then only for fun. For regular calculations I use an HP-11C. For teaching, I have to demonstrate with a TI-83/TI-86, though I don’t much like it. It is modern and capable, and everyone uses it, but I find it an awkward nuisance (Another blogger has a less charitable opinion of graphing calculators.) The algebraic entry system is inferior to RPN. The graphing features make the calculator too complex, but are not powerful enough to take the place of Excel or Mathematica. The size and shape make the TI difficult to operate. The HP’s horizontal layout makes it easy to hold while I push buttons with both thumbs, and the keys on the HP have a nice solid feel. The HP fits in my pocket. If I need graphing I’ll use a workstation.