The HP-16C programmer’s calculator.
The 12C financial calculator gets all of the love when it comes to HP’s line of reverse polish calculators (it’s the only one I still see in stores), but the 16C was by far my favorite. It was the only place that I could do stuff that my TI-89 couldn’t, most specifically performing all of your operations in any base you want (helpful because I used to work almost exclusively with A/D converters that would give unsigned 12-bit integers for their measurements).
Some of the other features, most of which I haven’t seen on another calculator:
- Integer and floating point math.
- Shift functions: Left and right, arithmetic and non.
- Rotate functions: Rotate a single position or N positions left or right, through carry or not.
- Left justify the bits of a word.
- Masking: Create masks to mask left or right N bits.
- #B: returned number of bits set in a word
- Multiply/Divide: Provided functions for multiplying single precision numbers into single precision or double precision results. Likewise, allowed single or double precision dividends.
- Bitwise Logic: and, or, not, xor
- Bit setting and testing
- Flag setting and testing: (user flags and overflow/carry)
There’s a great iPhone app emulator called Calc 16Cx ($1), and one called ClassicRPN ($15) that does the 11, 12, 15 and 16 models.