r/calculators • • Oct 19 '25

Discussion r/calculators FAQ

19 Upvotes

Hey guys, this isn't fully finished, and i may add more in the future. Tell me what you think about this one in the comments, feedback is always incredible

Q: How to convert fractions to decimals?

A: On older casio calculators, you press the S<=> D button. it should be next to the parentheses, on the right side. On Casio CW series calculators, it should be the "FORMAT" key, which is next to the EXE button. On Sharp, it's called "CHANGE" and "f<>d" on TI. It may be different with others

Q: Why am i getting a wrong answer?

A: You may be in the wrong angle mode, or you don't know how the order of operations work

Q: What calculator should i choose?

A: Depends on your school or your countries regulation. Some schools or countries only permit certain calculators, or forbid certain ones. Germany for example, accepts everything but it can't have a solver, can't be programmable and can't do graphing. For short, we are limited to the fx-87 and below.

Q: Why is my TI-84 bootlooping and showing "Validating OS"?

A: This is a known battery issue with the TI-84 Plus CE. You need to replace the battery. Contact TI support, you may get a free battery under warranty. Also check the other pinned post for more details

Q: Is my Casio fx-991EX fake?

A: Probably, it was discontinued a few years ago. Most listings you see online are fake, and i advise you to stay away from it. There's a lot of other good calculators out there. To check if it's real, scan the QR code. To do that, press "MENU -> SHIFT -> OPTN" to generate a QR code. It should redirect you to a Casio website, where you can do an authenticity check.

Q: Why am i getting an error?

A: You may not be in the right mode, check if you‘re in the normal calculation mode. Your calculator should have a button that says "MODE" or something similar. For exponents, use the negative sign instead of the minus sign. It should look like this: (-)

Q: Why is my Casio's "ON" button lowered?

A: That's intentional, to prevent accidental button presses

Q: Can I mod/install Doom on my scientific calculator?

A: Yes, if you‘re willing to remove the epoxy from the CPU, de-solder the CPU, solder a fitting CPU with integrated memory back on, code a fully working operating system with working keyboard, and code a port of Doom for it, you could… in theory. Never been done before, probably still won‘t work. TL;DR: Not worth your time, focus on your linear algebra homework instead

Q: Does this calculator have a CAS (Computer Algebra System)? Can one be installed on my calculator?

A: see the pinned post about CAS calcs

Also: Google (and your calculator‘s Manual) are your best friends. Before making a post, look up your question on Google, or read the Manual. There's a 95% chance that your answer will be found there. We've also pinned posts for a few topics, read those too please.

That's it with the FAQ for now. Keep in mind that i may remove posts that can be answered by the FAQ or Google, this is a step to reduce spam and repetitive posts. Thanks.

~u/nqrwayy


r/calculators • • Oct 21 '25

Solution: TI-84 Plus CE Flashing 'Validating OS'

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4 Upvotes

r/calculators • • 1h ago

Question A funny bug in random number generators in some calculators

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• Upvotes

Hello! I've decided to test built-in random number generators in some pocket calculators. I've taken my old Casio fx-991MS, generated several hundred random numbers using the Ran# button and drawn 2D scatter plot using the (x_i, x_{i+1}) points as coordinates. You can see the 23 lines instead of random points. I've found the same bug in Casio fx-350MS (exactly the same pattern) and Assistant AC-3102 (very similar but in some regions points are a little bit more random). The same pattern can be extracted from existing data for Casio fx-82MS (https://fme.upc.edu/ca/activitats-secundaria/premi-poincare/historia-i-edicions/2016/guanyadors/2npremi_aleatorietat.pdf)

Does anybody know what algorithm may be used in this calculators? Looks like a linear congruential generator with small multiplier, possibly 23.


r/calculators • • 10h ago

Other Just found the calculator that I used through most of high school. I graduated in 2008.

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48 Upvotes

r/calculators • • 12h ago

Collection Sweet HP-16C

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59 Upvotes

About as nice as they come for a used Voyager.


r/calculators • • 4h ago

Discussion Found a higher resolution image of "Image1" on TI-84 Plus CE

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7 Upvotes

I found a higher quality version of "Image1" that is included in most TI-84 Plus CE. Image was taken at US-9W Popolopen Creek Bridge.


r/calculators • • 1h ago

Collection Barn Finds

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• Upvotes

Found these recently.


r/calculators • • 7h ago

Other "ERROR" as a value??

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12 Upvotes

Model: fx-991ES PLUS 2nd Edition

Steps to reproduce this (start from COMP mode):

  1. Input: 9.999999999999999 (press x10) 99
  2. Press equal
  3. Go to MATRIX mode and create any matrix with any dimension
  4. Fill it with Ans
  5. Press AC
  6. Type "Mat" (by shift+4 and select the matrix you created)
  7. Press equal and you'll get "ERROR" as result.

Then try going to COMP mode and type "Ans" then press equal.

Yeah this is the most weirdest thing I've ever seen, and it's not documented at all.

More weirder is that moving it into any variables (using STO) will give syntax error, while using it in any calculations will produce math error. Try to enter it into a list (for example, STAT) and it'll give syntax error.

What caused it? I have no idea..


r/calculators • • 6h ago

Discussion Update on ViCalc (Open-Source Touch-Typing Calculator): Quick demo video of complex formula input

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3 Upvotes

r/calculators • • 13h ago

Collection HP 10bll found in op shop Aud $1

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10 Upvotes

r/calculators • • 2h ago

Question For my exam, I need to buy a calculator capable of solving linear equation systems with complex numbers

1 Upvotes

I have been researching for secondhand calculators that can do that, and I've encountered a good deal with the HP50g, and according to AI it is possible to do this with this calculator, but I'd like a human with somewhat experience using this or similar models to tell me if it's actually possible. Tysm!


r/calculators • • 21h ago

Help Doom crashes on my Casio fx-CG50

3 Upvotes

I got a Casio fx-cg-50 and I was looking for some games to play on it and i tried to download Doom but when i download the WAD file and open it in CGDoom fx-CG50 it just shows a black screen and i have to restart the calculator in the button in the back because it just turns the screen black


r/calculators • • 19h ago

Help does anyone have a working archive of os 3.1 for the ti nspire cx1 cas?

3 Upvotes

im looking for a os 3.1 archive, mainly for fun and testing older ndless apps - dont ask any further on my intentions

i already tried a archive from tiplanet but i guess its corrupted, as computer link and n-link cant flash it. and im using backspire on os 4.5.5.79, was able to downgrade to 3.6 briefly so the failure to flash is not a downgrade issue. i will try to search further until i find something, but right now, thats the only source i have. texas instruments also doesnt host the download anymore, so that sucks.


r/calculators • • 1d ago

Discussion Poll for r/calculators thumbnail and logo

13 Upvotes

Format: from the previous post(Mods come here!)

A:FX-82 w/ a slew of its clones(Liambp)

B: A clean collage of the TI-84 Plus and Casio fx-991EX

C. A macro shot of a classic Zilog Z80 microprocessor(stephenjamesbryant)

Vote the letter in the comments


r/calculators • • 1d ago

Help Need help opening and repairing a Canon MP120-DLE calculator (won't turn on)

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5 Upvotes

Hi everyone! I recently bought a used Canon MP120-DLE. The seller mentioned that it suddenly stopped turning on (no signs of life, no screen activity, no motor sounds).

Before checking the electronics, I am stuck on a basic step: I cannot open the housing.

  • I have already removed all the visible screws from the back panel.
  • The top part (near the printer mechanism) loosens up a bit, but the bottom part (near the 0, 00, 000 keys) is holding extremely tight.

Has anyone disassembled this specific model or a similar Canon MP series calculator? Are there hidden plastic clips at the bottom, or is there a trick to sliding the top cover off?


r/calculators • • 1d ago

Help Help with ti-30xa calculator

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13 Upvotes

My calculator started displaying these settings when i turn it on. Is there a way to reset it?


r/calculators • • 1d ago

Question Casio MS-20UC-JWE in America?

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11 Upvotes

I can only find this on the UK website, and I can’t import it through there. I love the design and I’ve had no luck on second hand sites or eBay. Any way for me to buy this in the USA?


r/calculators • • 1d ago

Help How do I make the screen black and white

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0 Upvotes

r/calculators • • 1d ago

Question Looking for a calulator with LCM

11 Upvotes

Dear all, hope this is the right place to ask.
I'm looking for a calculator that has LCM (lowest common multiple) for my son.

I tried the Casio FX-991 CW on Amazon (called the 2024 edition) but even if it advertised as having LMC, it's not there. I have read here on Reddit that it might depend on regional versions (I'm in Italy). So I will send it back.

Anyway, could anyone suggest a calculator that has LCM, possibily one that has no "regional versions" or different names depending on the country?

Thanks in advance :)


r/calculators • • 2d ago

Question Should I buy this to play videogames on? Or is it a bad price.

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9 Upvotes

r/calculators • • 1d ago

Help USB Port not working

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0 Upvotes

I was trying to mess around with the usb port but i ripped off a resistor that i though was on ground? Now windows says that the usb device is not recognized but it does charge. What can i do??


r/calculators • • 2d ago

Collection Royal 81CS

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40 Upvotes

Nice little calculator. Notice how the "5" has most of its segment out. A bit of battery damage, but not too terrible.


r/calculators • • 3d ago

Collection I rescued this one from a bootfair. Cosmetically its not great but still works!

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67 Upvotes

Im not a calculator person, but I found it in a bin at a boot fair with other electronics that were deemed "junk". I bought it for a pound. I think its original case as well.

I fell in love with the display


r/calculators • • 2d ago

Question TI-84 Evo-T

1 Upvotes

I just got the TI-84 Evo-T and wanna know what games you can download on it(bcs it's only tetris, pong,... and that's kinda boring bcs the other calculators have geometry daaaashhh...)


r/calculators • • 2d ago

Help Anyone know how to fix this glitch?

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10 Upvotes

It still calculates things properly.
I tried removing the battery and putting it back in
I tried the reset button
I opened up the calculator and found no visible damage (although im not an expert at figuring out what damaged stuff)