10BII Calc HD Seems to be the best>Good Job!
10BII HD works great with older iPhones (4, 4S, 5, 5s), but one of the reviews said no 6, 6s support ---That I dont know: currently using a 5s with iOS 10.
I have used this calculator of Ernest Brocks for at least 5 or 6 years, in all the versions (on an iPhone 3G, 4s, 5s). I purchased all his financial calculators to test them out, but this is the one with the layout and key functions that I personally like to use. Mr. Brock has added in very easy prediction and amortization to the functions of the original HP hardware calc. The calculations are always perfect (Ive purchased about 20 calc apps with weird errors in calculation), and this app has features and ease of use that go way beyond the "real" HP 10BII and my other hardware business/financial calculators (including an original HP19IIb, for calculator geeks).
(side note: for a scientific calculator I use TLAs pCalc. Ernest Brock owns the financial calc realm, but I like the pCalc scientific functions.)
For the 10BII interface, Ernest Brock has picked some easy to read colors for button labels, and when you enter a new current/future amount, interest, etc, the entry appears in little but readable (Im over 60) bright numbers below the keys. There are periodic useful improvements/ upgrades, that actually add to the usefulness and interface. In all the ways Ive used this calculator (bank accounts, mortgage, student loans, etc), NO GLITCHES!
alwaysmprest about
10BII Calc HD, v2.4