fx-991MS 2nd Edition:
- Nice adjustable high-contrast display (although it's lowest setting isn't low enough IMO).
- Crisp and easily readable printing on the front panel and buttons. Very much like the brown grey texture and colour.
- Engineering symbols as shifted functions on numbers.
- 15 digits of precision instead of 12 for the first edition.
- Improved differentiation accuracy (probably due to the extra digits).
- Fast decimal to fraction conversion (as compared to the first edition MS series).
- Quicker simple calculation answers. As an example if you were to set up a chain calculation and rapidly press the [=] button it takes time to recieve an answer, so not every press is registered. The old first edition seems to max out at ~4 answers per second, while the new 2nd edition is noticably quicker at ~8 answers per second.
- Newer constant data (CODATA 2010 vs 1998)
- Multi-statement feature (1st edition feature) is pretty neat. In combination with the [CALC] function, you can separate the two x & y components of a parametric equation with a colon and enter the parametric variable to see how both equations change.
- Replay-Copy function (1st edition feature) allows you to replay the calculation history from a chosen point, to either correct errors, or store past answers (Since the answer variable is updated after most operations).
- Converts reoccuring numbers to fractions (2nd edition feature). From some rough testing when going beyond about the 13th or 14th digit (eg 0.333 333 333 333 3 can be converted to 1/3, 0.666 666 666 666 66 to 2/3).
- Flimsy construction, creaks when twisted lightly. Hardcover is poor fit and wobbles and rattles when pressing keys when clipped into the hardcover in one of the two orientations. LCD is affected by small amount of force on housing near display. My old fx-95MS and the smaller and thinner fx-991W are much sturdier in construction.
- Relatively big for a 2-line calculator with plenty of wasted space. Could of easily put in an additional 2 buttons if they moved up the navigation controls (A dedicated recall and store button (as on the fx-991W), is convenient).
- Power consumption hasn't improved over older calculators. My old fx-991W solar cell can be powered off a weaker light source than the fx-991MS 2nd edition. One of the primary reasons I purchased the fx-991MS 2nd edition was the reduction of the power consumption from 0.0002W -> 0.0001W (same as fx-991W). I was hoping for better low-light performance with the solar cell, but was disappointed to find that nothing has improved in the 20 years since.
- Multiple page menu system. Some functions require navigating several small menus to get to, where pre-VPAM calculators like the Casio fx-100D had functionality that could be accessed directly from the keyboard (eg the line above the calculator listing all the different modes).
- Does not save calculation history on power off, and non-adjustable auto-power off timer (Casio should at least provide an option for 60 minutes).
- Can not store the displayed answer for a calculation; instead it executes the displayed calculation again and then stores the answer from that (Since this result is in memory as can be seen on the second line, it is bizzare that you can't actually copy the displayed value to variable memory).
- Can not store answers while staying in CALC mode (unlike the older fx-991W)
- Can't handle complex powers very easily (it can be done, but using a combination of squares and cubes).
- Still using old Simpson integration method (although the algorithm seems to be updated from some testing, it is still much slower and less accurate than the Gauss one used on the fx-991ES/991EX)
Worth it or not?:
I was looking for a companion calculator to my Casio graphing calculators (fx-CG50, fx-9750G2), that would have quicker access to some of the more simpler functions that are often buried deep within menus on the graphing calculators. In addition I was also hoping for something that was low-powered enough that the solar cell was a useful addition rather than a gimmick (One of those usually less important requirements that I put an unusually high value in).
One of my problems with more modern Casio scientific calculators is their tendancy to move functionality from keyboard shortcuts to menus, often at the expense of convenience. For example Casio's last direct entry (non-VPAM) calculators were released in 1992 (D-Series, I have the fx-100D from that era), where all of the modes were printed at the top of the keyboard and only required 2 key presses to change. With newer versions (W or MS series), you have to keep pressing [MODE] to get to the correct small menu and then press the appropriate number. In contrast the fx-991EX has a single menu where all modes have a number shortcut, meaning with practice switching modes should be just as quick as the old fx-100D.
The fx-991MS menu system is particularly bad with Statistics mode, where recalling certain statistical functions (especially regression) requires navigating through many small menus just to get a single function. Once again the fx-991EX does better here by displaying all of the statistical information for entered variables on the same screen, saving many key-presses.
The decision that lead me to purchasing the fx-991MS 2nd edition, was probably my poor experience with the fx-115ES Plus (bad contrast, sluggish menus, and I didn't like it's overall design), coupled with a positive usability experience on an old second-hand fx-991W I had acquired. I also have to admit that part of it may of been the nostalgic look of a great contrast, 7 segment display as opposed to an all dot-matrix one.
While I don't own the fx-991EX, I do wish that in hindsight that I had of understood the difference between a calculator that looks simple to use (fx-991MS 2nd edition), but has a badly implemented menu system vs a complex looking calculator (fx-991EX) with a more intuitive menu design.
Some things I would change to make the fx-991MS 2nd edition better:
- More compact, less wasted space. The fx-991W is a great example here, thinner and shorter, while buttons are spaced the same distance horizontally and vertically (I didn't believe it until I put them side by side and bottom to bottom). On top of that, the smaller more compact case on the fx-991W is much less flimsy.
- Shift navigation button up, add 2 additional function keys with one of them being a dedicated memory recall function.
- Gauss Kronrod integration. The Simpson implementation on the fx-991W (1998) is hugely impressive, but it's slow and inaccurate for a 2019 calculator.
- Removal of mode selection menus. For example with pre-VPAM calculators (eg my fx-100D), Mode selection is printed at the top of the keyboard, so all modes are 2/3-key presses away.
- While in Base-N mode, placing all logic functions (AND, NOT, XOR, etc) back on to the keyboard (the menus both complicate and slow base-n operations down, the fx-100D does this much better).
- Statistics functions removed from menus and placed back on keyboard. The fx-991EX may use a menu system, but takes advantage of it's high resolution to show you all statistics variables at once, unfortunately, with the fx-991MS you need to tab through multiple small menus to get what you want, select it, then press equals to finally show the data. The older fx-991W I have is also faster and easier to use, since desired statistics function are directly accessed from the keyboard via .
- When storing numbers (from recent or prior calculations), store the displayed answer!. It's crazy that you can see the result of a calculation (shown on the second line of the fx-991MS), but you can't store that number into variable memory. When you store a value from the calculation history, it doesn't store the displayed result, but instead executes the calculation again and then stores the result of that. Especially infuriating for chain calculations (ie utilizing the ANS variable which is updated after almost every operation).
- Persistent calculation memory. This in combination with the unadjustable auto-power off makes the calculation history a bit pointless. 10 minutes is a bit better than the 7 minutes on the first edition, but in my experience I find that the calculator turns off between calculations. Either make it persistant like the Casio graphing calculators (or the Sharp EL-W516X), or allow adjustment of the auto power-off feature to 1 hour.
Overall, I wouldn't recommend the fx-991MS 2nd edition, at least not unless you can purchase it noticable cheaper than the fx-991EX. If I could go back knowing what I know now, I would of probably chosen the fx-991EX (I would of prefered the fx-570EX with it's AAA battery as it has significantly more capacity than SR44/LR44 battery, but for some reason it is nearly double the price of the fx-991EX), or saved my money and continue using the second-hand fx-991W that I have.
I haven't completely given up on the fx-991MS 2nd edition, and still think that the mult-statement system might still show it's value in the near future, however considering the price I paid was the same as the fx-991EX, for mediocre quality construction with very little improvement over the first edition (I think the first MS was released in 2001) I think it is poor value for money.
Edited by MJim, 21 February 2020 - 07:26 AM.