Casio FX-991ES Scientific Calculator

This model, together with the FX-570ES, are the most advanced scientific calculators in the current Casio range. The two models are identical, except that this one is powered by a solar cell and a small LR44 button battery, while the other requires an ordinary, cheap, AA torch battery, which I think is preferable. At last calculator manufacturers seem to have realised that lithium batteries, at retail prices, eventually cost more than their calculators.

Another great improvement from earlier models is the keyboard base, which is now silver and so far easier to read in any lighting, than the previous Casio favourite, that awful black, which was impossible to read at home at night. The key action is very good, soft with a slight click, as we have come to expect from Casio, but I would still prefer it slightly softer, as in some earlier models, for faster operation. The calculating facilities it offers are excellent: 403 functions, including solve, calc, 3 simultaneous equations, matrices, bivariate regression etc, plus the dubious benefit of 40 constants.
The finish and workmanship are first class.

But excellent though this model is in all the above, it does have some disadvantages compared with previous models, which prevent me from giving it an "excellent" overall rating. The main one is that it has no programmability at all and so it is more suitable for schools and collages, rather than for serious professional or scientific work. -The grafic models are not the answer as they are big and heavy, difficult to learn and much slower to operate-. Another shortcominbg is that it omly has 7 memories, and storing numbers into them is clumsy and slow, requiring 3 key strokes on distant keys, instead of the usual 2. So does fixing the number of decimal points. Its logic with memories is also less efficient than previously. It is a pity that manufacturers so often take 2 steps forward and 1 step backwards. I hope one day Casio will correct these shortcomings and they will then have a world beater. My rating is: "Very good"

This was an upgrade to another calculator i had the FX85ES and having this calculator through GCSE and maths at a-level made my life a hell of a lot easier. When it came to further maths at a-level, involving sigma notation and integrals, i was resorting to a graphics calculator and imaginary numbers had to be done in my head or on paper. On coming accross the FX-991ES it once again made my maths lessons and exams a hell of a lot easier, the natural display ensures no brackets are missed and the use of numerical differentiation and integration makes calculus with limits easy to check. The use of imagianry numbers also goes a long way too. It also has an equation solver which can solve almost any equation with one variable, saving time checking answers. The best part is it isn't illegal in any of my A-level exams, so happy days.

This beautifully made calculator has 403 functions and can do not only numerical integration and regression with two variables, permutations and combinations, but also has a "solve" function for equations and can also solve simultaneous equations and matrices.

The key action is perfect, as we have come to expect from Casio and thank goodness the lettering is black on white and not that awful yellow and red on black (a Casio favourite), which is so difficult to read at home at night. This model is solar powered, supported by a small button battery(much less expensive than lithium). In all other respects it is identical with FX-570ES which is not solar but uses one standard AAA torch battery and sells at the same price. It remains to be seen which model will prove more popular.

But perfect though these two models are for what they do, they have one important deficiency which prevents me from giving them an "excellent" score. They are not programmable, which means they are designed for school and college work rather than for serious scientific or professional work. What a pity!

I have bought the calculator so that i can use it for my orindary level exams and later for the advanced maths. I like its features and its large display which could show the fractions (for example) with the numbers on top of each other. The only two things i don't really like are that there are two less variables than other calculators by Casio and that the manual is on a large sheet not a booklet. I still like the calculator very much and would still give it an excellent rating. Also, the constants and conversions could be utilised. All in all, I'm really happy with my casio fx-991ES as it makes my life easier drawing tables and solving equations etc!

2 Years after we bought this calculator for our eldest daughter, we have bought an identical one for her sister when she started secondary school.

We think that this is the top of the range of the "normal", non-specialized calculators in the market. It is easy to use and the natural textbook display is brilliant, especially if your child is still learning how to do specific calculations: it displays the calculations exactly as it is written in the books, which makes it easier to spot mistakes and learn from these mistakes.

The calculator is sophisticated enough to grow with your child and while in school (and further on) they will not need another calculator.

The calculator both works with batteries and with solar power, which makes sure it is always ready to use.

I really can't think of anything that I would like to change, I can fully recommend this calculator!