Here's my favorite Droid app so far. It's an RPN calculator from Brain Overspill. Though not an HP emulation, they've taken the best of calculator UI / PDA design and combined it with an RPN option.
Though I'm not a fan of long press, in this case it's faster than using shift. For instance in conversion, enter a number (or result of calculation) then hold down the EXP key (not show in outdated photo). A dialog pops up. Select units and it displays all the other forms - very quick and easy.
As noted above, the picture is outdated and also in Algebraic mode - they also have %, Rotate and Swap XY. When they get around to financial and stat functions, it'll be perfect. Nice work guys.
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