Summary: HP has a long tradition of building outstanding scientific calculators. The HP 35S continues that tradition. The operating system that controls calculator modes and menus is intuitive. The RPN system for evaluating mathematical expressions is just unbeatable. It is much faster than algebraic systems. It is much less prone to errors. The calculator is rugged, sleek and attractive to boot.
Summary: My experience with HP calculators includes using an original HP-35 some forty years ago when the model was new. It was an amazing encounter as up until that time one had to employ slide rules and books filled with tables of function values. Learning RPN was easy. My only discomfort was the disappointment that I didn't think of it first. My first HP calculator I bought for myself was an HP-25.
Summary: I've used HP's since the 80's, loved the 34C and my 11C. Unfortunately lost the 34C and used the 11C for over 20 years until last week when the display couldn't take commercial travel in unpressurized baggage compartments. Now I'm stuck with this 35S piece of garbage that I bought over a year ago and through in a drawer. I'd come to expect unequaled quality and performance of HP calculators and they don't offer anything close to the old 11C or the 34C keyboard feel.
Summary: This one is my favorite so far. I have bought several. The calculator is very easy to use, has lots of memory, easy to program, and provides marked improvement in the area of complex number operations compared to the hp 32sii. As a EE I really appreciate this. The dedicated "i" key is a dream come true for an Electrical Engineering type like myself. My only complaint has to do with keyboard quality in terms of missed keystrokes on some units.
Summary: The keys on this calculator are horrible and start to malfunction within 4 months of owning it. They require too much pressure and do not hold up to constant use. I cannot rely of the results that I get. I have to double check (sometimes triple check ) my results. The keys are too hard and only respond if pressed very hard. I do like the layout and the appearance of it - I only wish that it worked better.
Summary: RPN calculators are hard to come by any more, but this one is just perfect. I actually am replacing my HP50g (~$150) with this one. For one, the 50g died after only 5 years and I didn't want to spend another $150 to replace it for the same thing to happen again. Hopefully this one lasts a lot longer. My TI's from H.S. still work 15 years later. But since then I have grown accustomed to RPN and don't want to go back.