Free42 4+

Yep. Seriously.
This is one of the very best calculators available for download on the internet.
As a FREE app, perhaps only the Wp-34S and a handful of others come close; and the few that do are almost exclusively based upon ground-breaking machines produced by Hewlett Packard.

Highlighting Free42's capabilities could fill a small book - and it's better than the machine it's based upon! Thankfully, manuals, web-sites and forums exist to support this magnificent piece of work, and although exploring the wealth of information is not essential, it is educational and highly rewarding.

Different skins are available too. They can be swapped in seconds, even during a calculation. And not only do they alter the appearance; in many cases they make subtle modifications to provide quicker access to various functions.

Bottom line:
Hundreds of calculators can perform basic arithmetic; but some do a whole lot more…

I love that this app is available on iPhone.

It’s have a HP-42s and a DM42 but this is super handy on my phone.

The haptic feedback, button press sound and that the buttons move when you press them are all great little touches.

If you are familiar with the 42S this is for you. If you are interested in learning to use an RPN programmable calculator this one is very well documented and easy to program so it’s a great place to start.

Would be nice to have an additional skin which makes better use of the empty space, and the ability to view all registers etc.

Respect to Thomas for creating this... and making it free, to boot. Brought back many memories, so much so, in fact, that I decided to spring for a real HP 35S on eBay to replace my stolen 42S! Just one small suggestion that would make this truly awesome: imagine being able to see all five registers – X, Y, Z, T and L on the screen at once...