I have just bought myself a new scientific calculator, a Casio fx-991CE X CLASSWIZ series, which is a twin of fx-991EX adapted for central Europe. This new inventory items serves as a replacement for my old 991ES, which got slight damage on the LCD display. It is still almost perfectly usable but sometimes a little bit harder to read on it's right side, which is getting more and more irritating.

During my studies at university, I had many many semesters that made a direct use of the 991ES. Almost every class I attended got some part which could use some function of the endless array of functions it provides. Be it mathematics, which I had total of 13 classes, electro and electronics, physics or even material sciences. Thus I made sure I know and understand it's functions very well. I was carrying the printed manual around and studies it when I had some time in the class.

Now the motivation to chose the successor to 991ES was to be something that is very similar, but newer. I was able to pick up a few new functions 991CE X has over 991ES in under an hour. Most notably the [FACT] function, which does split numbers to their respective factors (conditions apply) and a mini spreadsheets editor, which is pretty impressive, given the fact this is a calculator.

When it arrived, I wanted to note it's serial number into the list of equipment I curate. And hereby lies the problem - I could not find it! It was not on any sticker on the box, it was not on a sticker on a calculator itself, it was nowhere to be found in the battery compartment, nor it was in its bowels when disassembled.

QR Code function

Apart from being much faster and having four line display, instead of two line which is the case for 991ES, the 991CE X has another new trick up it's sleeve: QR code generator.

The QR code generator is primarily intended to share results, formulas and even spreadsheets with the outer world. The request created by QR code first goes to casio.com, specifically wes.casio.com, and then get's redirected to classpad.net, an external service operated by Casio. This is a correct procedure when creating links to somewhere - always first point the link to something you are sure will be controlling in the future, an only then redirect somewhere else. Should Casio at one point sell or shut down the classpad.net, they would lose control if they pointed the links straight to it right away.

Anyway, by searching around for information about how to dig out the serial number of the calculator, I firs stumbled on an official authenticity check, which confirms if your device is original and genuine and not a knock-off. Here's how it works: you press [MENU] and then [SHIFT] + [QR]. This creates a request that again point to wes.casio.com and looks like this:


All the segments marked by Q, X, Y and Z letters are alphanumerical and all except the Y segment were hexadecimal. I thought that maybe the serial number is one of these parameters but I could not tell for sure. I thus marked this link as a "serial number" into my list and went on with my life.

YouTube algorithm to the rescue

The next day I was looking for some other information on YouTube when suddenly between my suggestions there was a video named Casio calculator fx-991EX hidden diagnostic test mode functions. I must admit I have never know about this diagnostic test for Casio calculators. Since it is "hidden", it was obviously not in the manual and it never occurred to me to search for such feature back then.

I was curious, the video was around 2 minutes long, so a took a change and clicked it. Oh boy, it was a golden nugget hidden in a plain sight. The video starts with the basic display and keyboard diagnostic test initiated via pressing 7 + [SHIFT] + [ON] together. Now pressing 8 initiates screen containing the following table:


By pressing the corresponding keys you can match all of them and after it the calculator displays the message Solar MODEL OK!. By pressing [AC] now the calculator returns to a normal operator. This is not terribly interesting. However the video goes on.

Diagnostic modes

As it turns out, the 991EX or 991CE X, has at least two diagnostic modes. Another one is initiated by pressing 7 + [SHIFT] + [ON] but then continuing via pressing 9 this time.

This time the display prints out the 8.8E15. By pressing [SHIFT] multiple times, it then lands on the following:


Press AC

Interestingly, the QQQ segment matches the number from the link to the authenticity check. Now, as seen in the video at the 1:37 mark, by pressing [MENU] the following screen can be seen:

P00 Read OK
Press AC

VerF should be marking the latest version, at the time of writing. Now the only thing we need is to pres [AC] one more time:

[Serial number]

Bingo! Curiously, this information is presented in, for a 991CE X, an unusual three-line display mode. However, this number matches the X segment from the link. The serial number is sent as is there! Unfortunately, I have not found what are the data from Y nor Z segments for. The Y is almost all zeroes, but the Z contains probably some check sum, otherwise it appears to me they could be validating the authenticity entirely by the serial number and version alone, which seems unlikely. Especially given the fact that they are sending these four segments. But the Z segment does not match the A segment from the previous diagnostic screen, and this one probably is some check sum, given the word SUM that precedes it.

Keyboard check

By pressing the [AC] one more time, the display shows 00 and it is now in keyboard check mode. This is not a terribly useful mode as it does not present any additional information to us. I have found out this mode is very similar, if not identical to the diagnostic mode for 991ES. However the check procedure itself if weirdly unintuitive, so for those playing along at home, it is worth checking out.