Yes, calculators are made from plastic ^^

[Stefan]

@HP67
I recently got a fx-991ES Plus because all but one of my calcs are not allowed on my next exams. (The one I have which would be allowed is the fx-991MS, but this doesn't have the "natural display" which I don't want to miss after getting used to it).
I'd say the 991ES Plus is an okay calculator. It feels cheaper and not so robust compared to the earlier casios like the fx-991MS.
The worst thing about the 991ES Plus is that if you enter big formulas, the input becomes so sluggish that it misses key presses. So better don't type too fast ;-). Although I read somewhere that the *Plus* version of the 991ES should have fixed this "sluggish entry" bug, I think it's as bad as it was for the 991ES (without plus).
Also it looks like that Casio has removed the possibility to define Variables with the "=" sign as an alternative to "STO". This was possible in the 991MS and combined with the multi-statement operator ":" allowed tricks like described here, which comes pretty close to programming: http://nayuki.eigenstate.org/page/casio-...and-tricks
Another thing I don't like is that it looses entry history everytime you shut down the calc (Variables are retained though).
And to enter constants you *need* to know the number of the constant, which is written on the slide-on case. If you loose the case you are lost :-P

If I would recommend you a calc which has a comparable feature set, I'd say look at the Sharp EL-W506 (*NOT* EL-506W). Most important to me: It doesn't have the sluggish entry problem.
Then you have 4 user definable key shortcuts and 4 variables in which you can store expressions (which is why it is not allowed on my exams, because it counts as programmable *facepalm*). Furthermore it has engineering prefixes (like "n" for nano, "k" for kilo and so on).
All constants and unit conversions are listed in the corresponding menu, so you don't have to look it up on the case like you have to on the casio.
The Matrix mode allows 4x4 matrices (casio has 3x3), which gives one essentially the possibility to solve 4th degree linear equation systems.
The Sharp remembers everything even after shutting down. And the Font is a little bit smaller (but good readable) so you can display more on the screen.
Sadly it lacks the feature of multiple-statements. So you cant do those nice tricks either.

Another calc which I own and which has some more features than the fx-991ES Plus is the fx-991DE Plus. It has all the disadvantages of the ES Plus, but provides additional function to calculate prime factors (up to 4000 or so), GCD, LCM, additional statistic functions.
The DE Plus was especially developed for the German market (according to casio), but I think there should be an international equivalent. The annoying thing about the localization is that the decimal seperator is a comma instead of a dot. I find this very irritating, although I am German and hence usually write a comma on paper. But I got so used to reading a dot on a calculator that i find it really disturbing.

I think the HP-300s+ is *exactly* the same as the fx-991DE Plus, it has exactly the same features (minus the localization). Only the keypad is a bit different. (Does anybody have more information about that whether it is a contract work from Casio for HP?). It is cheaper (15€) than the Casio (21€), looks nicer and more sturdy in my opinion (But since I don't own the HP I can only judge this from the photos).

@Everybody who mentioned rubber keys: Right, I totally forgot those. compared to rubber keys, plastic is really a quality attribute ^^