Hacker News: MatthiasWandel

New comment by MatthiasWandel in "Why can't a gear have less than 17 teeth"

MatthiasWandel — Sun, 21 Dec 2025 12:32:57 +0000

A downside of profile shift is that you get away from the pitch diameter. At the pitch diameter, there's no friction on the teeth, the further away you get, the more friction. But any hand drill will have a gear with less than ten teeth cut into the motor's shaft to drive the first gear, and they work just fine.

New comment by MatthiasWandel in "An optimizing compiler doesn't help much with long instruction dependencies"

MatthiasWandel — Mon, 02 Jun 2025 01:33:16 +0000

The bottleneck with the pointer table may be the summation. While the fetches of elements can be parallelized, the summation can not, as the addition depends on the result of the previous addition being available.

Some experiments I have done with something that does summation showed a considerable speedup by summing odd and even values into separate bins. Although this applies only to doing something not too closely resembling signal processing algorithms, as the compiler can otherwise optimize out for that.

Part of my video titled "new computers don't speed up old code"

New comment by MatthiasWandel in "Performance optimization is hard because it's fundamentally a brute-force task"

MatthiasWandel — Tue, 29 Apr 2025 15:13:57 +0000

An interesting aspect is data dependencies. If your next statement reuses data you just computed, that can cause pipeline bubbles, as that result you want to use just isn't available yet. I dived into that topic for a video about relative performance of old PCs I just published today.

New comment by MatthiasWandel in "Making Software"

MatthiasWandel — Thu, 17 Apr 2025 13:45:31 +0000

nice, but spotted several inaccuracies on the landing page. perhaps not the best reference.

New comment by MatthiasWandel in "Switzerland's vinyl turntable roundabout: Unique road art (2019)"

MatthiasWandel — Thu, 03 Apr 2025 00:08:02 +0000

Disappointed to see the dots around it all appear to be the same spacing. They should be at different spacing, corresponding to strobe sync with 50 and 60 hz mains and 33.33 and 45 RPM. Hence four rings with different number of dots around the perimeter.

New comment by MatthiasWandel in "I Built a Mechanical Calculator [video]"

MatthiasWandel — Wed, 12 Mar 2025 23:11:07 +0000

I'm sure they would not have been less than £850 in whatever currency it was sold in back then, inflation adjusted. But the justification was much better than being a fidget toy.

New comment by MatthiasWandel in "“A calculator app? Anyone could make that”"

MatthiasWandel — Mon, 17 Feb 2025 12:26:29 +0000

The JVM based devices came years later. This was around 1998, with the 386 based blackbery pager that could only do emails over Mobitex, no phone calls. It even looked like a pager. At the time, phones were not so dominant, data switched over mobile only existed on paper, and two-way paging looked like it had a future. So we totally killed the crude 2-way paging networks that were out there. And RIM successfully later made the transition to phone networks. Wasn't till iPhone and android that RIM ran into trouble.

New comment by MatthiasWandel in "“A calculator app? Anyone could make that”"

MatthiasWandel — Mon, 17 Feb 2025 12:23:42 +0000

yes

New comment by MatthiasWandel in "“A calculator app? Anyone could make that”"

MatthiasWandel — Sun, 16 Feb 2025 21:12:18 +0000

I wrote the calculator for the original blackberry. Floating point won't do. I implemented decimal based floating point functions to avoid these rounding problems. This sounds harder than it was, basically, the "exponent" part wasn't how many bits to shift, but what power of two to divide by, so that 0.1, 0.001 etc can be represented exactly. Not sure if I had two or three digits of precision beyond whats on the display. 1 digit is pretty standard for 5 function calculators, scientific ones typically have two. It was only a 5 function calculator, so not that hard, plus there was no floating point library by default so doing any floating point really ballooned the size of an app with the floating point library.

New comment by MatthiasWandel in "The story of my home made pipe organ (2000)"

MatthiasWandel — Thu, 30 Jan 2025 16:58:38 +0000

Cutting away a lot with a router is a slow, noisy and dusty process. Less work to just glue together the channels out of smaller pieces of wood. Also, that way you can take individual pipes out and tweak them (called voicing).

Another thing to be wary of -- pipes too close together sometimes pull together in pitch if both are played at the same time.

New comment by MatthiasWandel in "How Unix spell ran in 64kb RAM"

MatthiasWandel — Sun, 19 Jan 2025 23:02:09 +0000

I remember spell checking my essays for high school on the commodore 64, using Paperclip 64, in 1984, Before there was ANY Microsoft windows. Spell check took a few minutes, because it read the dictionary from disk as it checked, and after that you could go thru all the words that it couldn't match.

New comment by MatthiasWandel in "Servo vs. steppers: Speed, Torque and Accuracy [video]"

MatthiasWandel — Wed, 15 Jan 2025 17:53:17 +0000

Actually not fair criticism, given that I even talk about changing the control parameters and demonstrate the effect of changing them.

New comment by MatthiasWandel in "Servo vs. steppers: Speed, Torque and Accuracy [video]"

MatthiasWandel — Wed, 15 Jan 2025 17:52:18 +0000

Please re-watch the video, but THIS TIME PAY ATTENTION. I do talk about the motion parameters, even show the code on the screen briefly. I even show the effects of changing the parameters.

New comment by MatthiasWandel in "Care Doesn't Scale"

MatthiasWandel — Mon, 28 Oct 2024 14:11:39 +0000

Things that scale can have a big multiplier, so to say. The problem is, more often than anticipated, that multiplier, rather than being large, ends up being considerably less than one.

Whereas work that doesn't scale always has a multiplier of 1, so its always useful.

New comment by MatthiasWandel in "Simone Giertz talks about invention"

MatthiasWandel — Wed, 23 Oct 2024 00:34:02 +0000

Since a daily activity once checked presumably never become unchecked, this could be just a big sheet of hexagons you can color in when the activity is done. Yes, you need to print out a new one once a year, but that's pretty trivial cost and time wise compared to the calendar gadget. Granted, the calendar is a cool gadget.

New comment by MatthiasWandel in "Centrifugal flows drive reverse rotation of Feynman's sprinkler"

MatthiasWandel — Sat, 27 Jan 2024 14:06:03 +0000

Ok, ascii diagram for my previous comment, indented:

    ===============
    Pipe  <---Suck
    ===============
               -----------vane-----------

New comment by MatthiasWandel in "Centrifugal flows drive reverse rotation of Feynman's sprinkler"

MatthiasWandel — Sat, 27 Jan 2024 13:39:01 +0000

regardless of what happens inside the S-curve, the opening ends up getting a slight vacuum from suction, but there is no such suction on the opposite side.

Imagine the S is straight, but a vane attached to the side of the pipe blocks suction from one side.

I tried to illustrate this in ascii art, but it appears HN has an algorithm to destroy ascii art.

That vane will now have a slight vacuum on the side of the pipe, and it seems logical that it should want to move in that direction.

Now imagine that vane curved around the pipe so it forms the end of the S-bend. Same thing.

New comment by MatthiasWandel in "The Magic of the Blackboard"

MatthiasWandel — Sat, 13 Jan 2024 14:58:33 +0000

chalk isn't a silicate. It's calcium carbonate. So no worries about silicosis. I think otherwise it would have been banned from schools long ago.

New comment by MatthiasWandel in "Leave work slightly unfinished for easier flow the next day"

MatthiasWandel — Fri, 15 Dec 2023 22:29:40 +0000

I have done something like that at times. I find the bug in the afternoon. Now I have the satisfaction of having found it and don't want to risk the frustration of it not actually being the actual bug I found. So I saved it for the next day, to milk the satisfaction again, but also to be more fresh at it to fix it right and test it, or to better be able to deal with it not being the actual bug! Though my boss at some point was puzzled "why don't you just fix it now?"

New comment by MatthiasWandel in "New research indicates social rigidity is a key predictor of cognitive rigidity"

MatthiasWandel — Sat, 15 Jul 2023 12:28:30 +0000

We use "science" to prove "they" are inferior.