Don't leave home without it
I consider the program of the MOST valuable ones on my iPhone...and wouldn't leave home without it. My wife doesn't understand why I need RPN for routine math, not to mention financial calculations, trig functions and statistics...but I do! When a recent "update" glitch, now resolved, left me without the program for several weeks, I realized how much I missed it, as I found myself trying to open it several times a day. Ultimately, getting it again operative, once I found the instructions on the developer's website, proved ridiculously quick and easy. A particularly nice feature for the Financial section is its nearly automatic generation of a full amortization or depreciation schedule. The one feature I would like to see in the next version would be operation in both the current vertical but also, the horizontal mode, the latter the way one uses the fabled HP11C and HP12C, which I have in the hardwired versions, but which I no longer carry, as allRPNCalc makes them superfluous, rather like a DC-3 in an Airbus 380 era.