Customer Review

Reviewed in the United States on September 26, 2017
At first glance, fx-991EX looks like a modernized version of fx-115ES PLUS. However, it has some shortcomings, compared to the predescessor:
1) Missing functions: LCM, GCD, Remainder division, Recurring decimals, and Product calculation - I have no idea why it was necessary to remove these important functions, so this is definitely a downgrade and a disappointment! Moreover, it turns out these features are available on some foreign versions of the same calculator, which leaves me wondering why the Casio marketing decided to drop them specifically from the U.S. version.
2) Usability: numbers are displayed in smaller font, which is harder to read; also the shift functions are painful to read on the black, textured, and somewhat reflective background.

At the same time, the new model has several obvious advantages over fx-115ES PLUS, such as:
1) a much faster processor (which is obvious when calculating integrals)
2) a new "QR" feature that can display graphs on your smartphone
3) a new "OPTN" button that can save you time
4) a separate "x" variable button that saves time
5) improved memory recall feature that shows all variables on one page
6) spreadsheet mode

Compared to the leading scientific calculators made by other brands (most notably Sharp and TI), my biggest pet peeve about Casio is that IT LOSES ALL THE HISTORY AS SOON AS THE POWER IS TURNED OFF. This is by far the biggest reason I stopped using Casio at work. As an engineer, I want to be able to return to the same formula I was working on after my calculator turned off due to inactivity. This should be THE most basic feature for any advanced engineering calculator, and I find it mind-boggling that the Casio marketing keeps ignoring it.

Other very useful and time-saving features that I would really like to see in future Casio calculators are: 1) a way to store and recall a few frequently used formulas, and 2) being able to jump to the beginning and end of the formula, e.g. by pressing Shift-Left and Shift-Right.

If Casio addresses my concerns mentioned above, I will be glad to consider this brand again.
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