GO-21 SciRPN 4+

This calculator was the best around in 1975 and saw me through college in electronic engineering. It is a RPN (reverse polar notation) unit that's is a powerful method of doing calculations without the need for brackets and "equal" buttons. Once one get used to entering the numbers on a stack and then choosing an operation, it makes for fast and logical processing.
In 1992 I up graded to a HP 48S which can do much more mathematics than I am able to understand. A truly wonderful machine, but with this comes complexity and is not as easy to use as the 21 which does almost everything I need. I love the HP 21 and glad I can enjoy it on my IPad.

I still have a working HP21 and use it almost daily - this app puts it on all my iHandhelddevices. It is just like the real thing - except with visible memory and stack (that you can hide under the calculator if you want to). I have bought several RPN calculators for iPhone - this is the first to not dissapoint.

Side note... The Hewlett Packard 20 series calculators (Woodstock) were released in the mid 70's, at the time they were state of the art technically and in terms of industrial design. HP developed far more powerful calculators, but the HP21 & 25 remain as a benchmark for pocket scientific calculators - it's worth getting a real one as well.

This RPN calculator is so realistic that it's like using the 1975 HP-21. Having the stack registers and memory displayed at all times is a bonus. The ability to move the calculator around on the desk top makes it suitable for left and right-hand use. How great it would be to have the HP-25 (same form factor) with its 49 programming steps visible, too. Hope the author considers it,