Today I am going to write my experience about my calculator, casio 991MS. I'm using this calculator for about 4 years, so i know the handy features. I am going to share it along with a test for original version.
How to ensure it is original:
Here is how you check the genuinity of your Casio 991MS calculator.
Press shift+7+ON button simultaneously,be sure you do not press one at a time or lost hold of any of the three buttons. If the calculator is original the screen will be changed, all pixel of the screen will go dark. Then press SHIFT button, the screen will be completely white, press it again and you will see broken characters, press Shift again and again broken characters appear. press it once more and you will see a number(in my case it is 25, but it may vary) with a OK text, pressing SHIFT again will show all 1 in display, pressing again will show all 2 and in this way it will show upto all 9. Then pressing it one more time will produce a 0 on screen, then pressing it will show a 1. Now press ALPHA, it will show 2, pressing MODE will show 3, pressing COPY left will show 4, COPY up will show 5, COPY right will show 6, CALC will show 7, integration button will show 8, LOGIC button and CONST button will show 9 and 10 respectively. Now press COPY down, it will show you 11. Pressing the buttons of next row will show later digits, continue pressing until you reach the "=" button. At this point you will see a OK text as you seen after broken characters.
One important point to remember, this security test has already been hacked and used in imitated calculators, but still we got one point in favor, drag your fingers overs the buttons from the second row to the last instead of pressing them one by one, if the test is still active, then you got the right calculator. At least it is original.
If you want to bye a Casio calculator of MS series, check it for the test. And if you want it from a trustworthy source, you can click here: Casio Scientific 2-Line Display Calculator fx-991MS Plus
It has a good screen with a solar panel, I do not know how well that works because I did not feel any necessity to change its battery or need to taste the power of solar panel provided.
Its keyboard is a good one with 20+22+1+1+1+1+1=47 button with about 400 functions. First 22 buttons are primarily numeric button with more shift and alpha options, they include scientific and statistics options. Next 22 buttons are purely used for functions and are placed in the upper portion of the calculator. These buttons provide equation solving feature, trigonometric, hyperbolic, calculation(calc button), logarithmic(both log and ln with anti-log and anti-ln). Last five buttons are shift, alpha, copy, mode and power on button.
Handy functions I love:
1. Finding value of one function for different values of variable using CALC function instead of doing it manually every time.
2. Solving equations- two or three variable system, also quadratic and cubic functions
It has one drawback, cannot solve complex equations.
3. Complex input handlers, I love it, it relieves me from hand computation.
4. CONST button, gives me values of common constants
5. CONV function, converts a lot any things for me.
I simply love it, it is very much handy, can be handled roughly without getting damaged, very much reliable, tension free battery and most important of all, fast enough and accurate for my engineering purpose. It is reasonable in price and serves better that you could expect. But I feel the necessity of a manual reset button, which I got in my previous Casio calculator. Though it provides option for software reset, I would like to have a hardware reset as well, of course as a back up.