The Rise Of Fake Casio Scientific Calculators

December 29, 2025 by Maya Posch 38 Comments

Scientific calculators are an amazing invention that take pocket calculators from being merely basic arithmetic machines to being pocket computers that can handle everything from statistics to algebra. That said, there are a few layers of scientific calculators, starting with those aimed at students. This is where Casio is very popular, especially because it uses traditional algebraic notation (VPAM) that follows the written style, rather than the reverse-polish notation (RPN) of HP and others. However, much like retro Casio wristwatches, it appears that these Casio calculators are now being (poorly) faked, as explained by [Another Roof] on YouTube.

The advanced fx-991 models are updated every few years, with the letters following the model indicating the year, such as fx-991EX standing for the 2015-released model. This was the model that got purchased online and which turned out to be fake. While the fx-991CW is newer, it changes the entire interface and is rightfully scolded in the video. Arguably this makes it the worst Casio scientific calculator in history.

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Only Known Copy Of UNIX V4 Recovered From Tape

December 29, 2025 by Maya Posch 43 Comments

UNIX version 4 is quite special on account of being the first UNIX to be written in C instead of PDP-11 ASM, but it was also considered to have been lost to the ravages of time. Joyfully, we can report that the more than fifty year old magnetic tape that was recently discovered in a University of Utah storeroom did in fact contain the UNIX v4 source code. As reported by Tom’s Hardware, [Al Kossow] of Bitsavers did the recovery by passing the raw flux data from the tape read head through the ReadTape program to reconstruct the stored data.

Since the tape was so old there was no telling how much of the data would still be intact, but fortunately it turned out that the tape was not only largely empty, but the data that was on it was in good nick. You can find the recovered files here, along with a README, with Archive.org hosting the multi-GB raw tape data. The recovered data includes the tape file in SimH format and the filesystem

Suffice it to say that you will not run UNIX v4 on anything other than a PDP-11 system or emulated equivalent, but if you want to run its modern successors in the form of BSD Unix, you can always give FreeBSD a shot.

The Birotary Engine Explained

December 28, 2025 by Maya Posch 34 Comments

Everyone generally knows about piston and rotary engines, with many a flamewar having been waged over the pros and cons of each design. The “correct” answer is thus to combine both into a single engine design. The resulting birotary engine comes courtesy of Czech company [Knob Engines] which makes their special engine for the aviation market. The workings of this engine and why it makes perfect sense for smaller airplanes is explained by [driving 4 answers] in a recent video.

Naturally, it’s at best confusing to call an engine a “rotary”, as this covers many types of engines. One could consider the birotary engine perhaps a cross between the traditional rotary piston engines that powered early aircraft and the Wankel rotary engines that would appear much later. The fact that both the housing and the crankshaft rotate reinforces this notion of a piston rotary, while it keeps the fixed ports and glow plugs on the housing that is typical of a Wankel-style engine. Having both the housing and crankshaft rotate is also why it’s called the ‘birotary’.

The claimed benefits of this design include a small size, low vibrations, reduced gyroscopic effect due to counter-rotation, no apex seals, and less mechanically complex than a piston engine. This comes at the cost of a very short stroke length and thus the need for a relatively high RPM and slow transition between power output levels, but those disadvantages are why small airplanes and UAVs are being targeted.

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Create Aerated Concrete Using Xanthan Gum And Dishwashing Liquid

December 28, 2025 by Maya Posch 29 Comments

To make aerated concrete, add a foam-forming agent and stir in a significant amount of air. This serves to make the concrete significantly lighter, better insulating, and more resilient to fire. Making it can however be a bit of an issue, often requiring ingredients that aren’t purchased at the average DIY store. This is where [NightHawkInLight]’s method seems rather promising, requiring effectively only xanthan gum and dishwashing detergent.

For the small-scale demonstration, 15 grams of the thickening agent xanthan gum is mixed with enough alcohol to create a slurry. To this 60 mL of the detergent and 1 liter of water is added and mixed until the xanthan gum has absorbed all the moisture, which takes about 5-10 minutes. This mixture is then added to Portland cement with two parts cement to one part xanthan gum/detergent mixture and mixed for a while.

Of importance here is that this mixture will keep expanding in volume while mixing, so you have to have to keep an eye on the amount of air relative to concrete, as this will determine the strength and other properties of the final aerated concrete. If you continue past a certain point you will even create open-celled aerated concrete that’s completely porous, so you have to know what kind of concrete you want before you start mixing up a big batch.

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Cloudflare’s Outages And Why Cool Kids Test On Prod

December 28, 2025 by Maya Posch 44 Comments

Every system administrator worth their salt knows that the right way to coax changes to network infrastructure onto a production network is to first validate it on a Staging network: a replica of the Production (Prod) network. Meanwhile all the developers who are working on upcoming changes are safely kept in their own padded safety rooms in the form of Test, Dev and similar, where Test tends to be the pre-staging phase and Dev is for new-and-breaking changes. This is what anyone should use, and yet Cloudflare apparently deems itself too cool for such a rational, time-tested approach based on their latest outage.

In their post-mortem on the December 5th outage, they describe how they started doing a roll-out of a change to React Server Components (RSC), to allow for a 1 MB buffer to be used as part of addressing the critical CVE-2025-55182 in RSC. During this roll-out on Prod, it was discovered that a testing tool didn’t support the increased buffer size and it was decided to globally disable it, bypassing the gradual roll-out mechanism.

This follows on the recent implosion at Cloudflare when their brand-new, Rust-based FL2 proxy keeled over when it encountered a corrupted input file. This time, disabling the testing tool created a condition in the original Lua-based FL1 where a NIL value was encountered, after which requests through this proxy began to fail with HTTP 500 errors. The one saving grace here is that the issue was detected and corrected fairly quickly, unlike when the FL2 proxy fell over due to another issue elsewhere in the network and it took much longer to diagnose and fix.

Aside from Cloudflare clearly having systemic issues with actually testing code and validating configurations prior to ‘testing’ on Prod, this ought to serve as a major warning to anyone else who feels that a ‘quick deployment on Prod’ isn’t such a big deal. Many of us have dealt with companies where testing and development happened on Staging, and the real staging on Prod. Even if it’s management-enforced, that doesn’t help much once stuff catches on fire and angry customers start lighting up the phone queue.

What To Do When Your Foucault Pendulum Stops Swinging

December 27, 2025 by Maya Posch 41 Comments

At the Houston Museum of Natural Science they recently made a disturbing discovery: their Foucault pendulum had stopped swinging for the first time since its installation in the 1970s. (Video, embedded below.)

While some might take this as yet another sign of the end times, here it is simply a sign that the electromagnetic system that kicks the pendulum developed a fault and will need to be fixed.

Their explainer video of this Herzstein Foucault pendulum is also worth watching, as it explains both the underlying physics and this particular pendulum’s construction. Every 48 hours the 81.6 kg heavy pendulum completes a full rotation, like clockwork, with pins along the circumference being tipped over one by one as the pendulum precesses.

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Active Ideal Full Bridge Rectifier Using TEA2208T

December 27, 2025 by Maya Posch 31 Comments

Everyone loves a full-wave bridge rectifier, but there’s no denying that they aren’t 100% efficient due to the diode voltage drop. Which isn’t to say that with some effort we cannot create an ideal bridge rectifier using active components, as demonstrated by [Mousa] with an active bridge circuit. This uses the NXP TEA2208T active bridge rectifier controller, along with the requisite four MOSFETs.

Comparing a diode bridge rectifier with an active bridge rectifier. (Credit: Mousa, YouTube)

Taking the circuit from the datasheet, a PCB was created featuring four FDD8N50NZ MOSFETs in addition to the controller IC. These were then compared to a diode-based bridge rectifier, showing the imperfections with the latter when analyzing the output using an oscilloscope.

As expected, the active rectifier’s output was also one volt higher than the diode bridge rectifier, which is another small boost to overall efficiency. According to NXP’s product page, there’s about a 1.4% efficiency gain at 90 VAC, with the chip being promoted for high-efficiency operations. When you consider that many designs like computer PSUs feature one or more diode bridge rectifiers often strapped to heatsinks, the appeal becomes apparent. As for [Mousa], he put this particular board in his laboratory PSU instead of the diode bridge rectifier, because why not.

Perhaps the biggest impediment to using an active rectifier is the cost, with the TEA2208T coming in at $4 on DigiKey for a quantity of 100, in addition to the MOSFETs, PCB, etc. If power efficiency isn’t the goal, then some wasted power and an aluminium heatsink is definitely cheaper.

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