HP 17bII+ software
This is probably one of the most underrated calculators in HP's current roster. It has everything one could need from a financial calculator, together with a very well laid out menu system. It has been proven: it has been running in the same style since 1989 if my memory does not fail.
The initial model was totally designed by HP, and was programmed in SysRPL. The current model has been made externally under HP contract, but the firmware was prepared by the producer, in order to fulfill HP's specs. This shows in the different approach taken for the solver. Functionally, both machines are the same, with the difference that the newer one includes an additional menu that takes care of currency exchange calculations. (this menu is of interest unless you have a smartphone, which provides updated currency exchange calculations on the fly)
It only misses the advanced mathematical features of the HP19bII to be perfect. By the way, these features are present in the HP30b, but there the user interface is not as slick as this one. And the way you can program the solver has not been equalled in my experience.
You just need to write something like:
(EBIT equals units times margin less personnel costs and less other costs)
The solver will create the corresponding variables, which can be edited at any moment. If you press a number and the menu key of the variable, it gets automatically stored in it; if you press it after another key that is not a number, the solver tries to calculate the value, based on the formula. And there you have a "program" to calculate the break even. you can use it now in boardroom meetings to get a fast idea about how long it will take until your start up starts making profit.
Same happens with the famous Black & Scholes formula. As far as I know, this is exclusive territory of the HP30b; but there are formulae prepared to be entered in the HP17bII, and even on the humble HP12c.
I would say that the main feature of this calculator is the solver, but the rest of the menus are organized in the same way. You can have different lists of money flows or statistical variables, and these lists can be saved, edited and recovered for further work, be it IRR and time value of money calculations, statistical calculations or regression of all kinds.
With the memory it is supplied (28 kbytes), there is no problem in programming additional functions like the trigonometric ones. This programming needs to be done in the solver. It is a pain to enter it the first time, but then you are rewarded with an even more complete calculator. I have never been over 7% use of the memory!
You can get a taste of the hp17bii by downloading the app 17bII+ Financial Calculator by RLM software. However, it is not free: 1 cent short of 7 €, in the Spanish shop.
You will not be able to appreciate one of the best keyboards available for a calculator. By the way, do not let anyone make you think that you smartphone is an alternative for your calculator. I have all free calculator apps, and some of the paying ones, including the ones from HP and the fantastic I41cx+; and while they are good enough to save you from a problem, they are no match for a proper calculator on your desk.