An expository talk I gave yesterday about Nielsen Theory. Nine variations! Should be accessible to anyone with a little topology background. (fixed audio from prior upload) youtu.be/8tJVWOXV1GU

New gizmo: 4D tape measure youtube.com/shorts/f5oqK...

In Spain if there’s a fire you dump this giant bottle of sriracha on it.

Yesterday I checked out El Rasto market in Madrid. Highlights: - two auto-numbering Bates-type stamps - fancy old stapler - abacus-like shipping list thing

Today’s yard sale find: a curved aluminum ruler and French curve. Looks like they could do some damage.

Progress! I’m shocked- it wouldn’t do anything 10 minutes ago! I still don’t really know what all the buttons do…

New old adding machine seems jammed. Should be able to pop the case and figure it out, right?

@itsmebenmarsh.bsky.social Did you delete your substack? I know I'm slow but I was planning to read "Serpent on the Mount" after I finished my other book last night. But now I can't find it!

New sign on the office wall. Don’t make me point at it!

I am on the list! (My dad too!) Probably everybody who publishes math papers. But the journal publishers own all the rights, so I guess they are the ones who would be compensated in a settlement?

who hurt you bro?

Dae-Woong Lee, P. Christopher Staecker Homotopy equivalence of digital pictures in $\mathbb{Z}^2$ https://arxiv.org/abs/2509.03023

Math props in Batman: Arkham Knight. Classic NCR inspired- not interactable, and the buttons aren't even 3D-modeled! Just painted on. And honestly I'm not sure why this is even here- the game is set in "present day". Some lore I'm not privy to I guess.

As I was walking home today, I had this idea: Is it possible to turn a QR code into a Truchet tiling that's still a functioning QR code? Yep.

Too rich for me but this is wild! I didn’t know this existed. ebay.us/m/CqmsIC

I just received this amazing set of hand-crafted wooden Golomb Rulers from Todd Sanders. (I made the much more pedestrian 3d-printed stand.) Thanks so much @lackriver.bsky.social‬!

Why do they always say "am I being detained"? Who made them think this is some kind of magic word? Is it some kind of magic word?

Just saw this listing for a really cool machine- with the ORIGINAL box! I’ve never seen the box before. Didn’t know there was one. It’s plastic but I love this machine. ebay.us/m/P8HG6O

Bought two peaches

Spotted today: Royal typewriter with homemade cover, and box o horns

New video: A "Trade Stimulator" from the 1890s! The direct precursor to the slot machine, designed to be legally ambiguous. youtu.be/ghy68syYtC8

This weekend yard sale curiosities: fully automatic craps table? Royal typewriter, strange 4-color style stitch work, and an old stereoscopic photo set.

NCR electromechanical cash register in the wild in upstate NY. Still in use!

Original!

Seen on reddit- very cool idea www.reddit.com/r/Sliderules...

slide that decimal point over and we got a deal

Weekend flea finds: Labubu AND Lobobo, those squirts water toys, and Nemo from Finding Nemo. Nuthin good though

U admin: It's OK to reduce our library's physical collection- we have beautiful licensed eBooks! Those beautiful eBooks: (not downloadable)

some youtube guy just followed me @vsauce.bsky.social

“Staecker”. And “Korean finger counting method”? Have I taught you nothing?

There’s a set on eBay now! But $55 seems a bit much- you can get the whole box new for $75, minus 25% with my promo code!

Nice abacus but cmon now

New video: slide rule chopsticks! youtu.be/xIMwnBZe4Xw

Finds today: very nice chart recorder! But the door is jammed- was $2 too much for me to pay? Also a TI-30 with original zipper case.

Estate sale boxagears

Nice writeup here- thanks @hackadayofficial.bsky.social hackaday.com/2025/07/09/k...

I got a mention in @tomscott.com Tom Scott's weekly newsletter- thanks to my new best bud!

My most ambitious video project ever. The story touches on lots of big themes and for me is genuinely thought-provoking in many ways. And it's a story that I don't think has ever been told before. I hope other people will find it interesting too. #chisanbop youtu.be/Rsaf4ncxlyA?...

There’s a difference between appreciating your country and idolizing it. Patriotism invites accountability. Nationalism shuts it down.

A new paper computer by Ryan Buss! With javascript simulator. #papercomputers papercpu.dev

bro in front of me has 51 stars on his shirt

“We have guided missiles and misguided men.” - Dr. Martin Luther King Jr.

Fully funded after 48 hours! Congrats Jesse!

New video: review of a new kickstarter project ROONS, a programmable marble computer. #turingcomplete www.youtube.com/watch?v=8taE...

Weekend flea find: a “Log scale” ruler that is not what you think. It’s for measuring wood logs.

hotel soap indeterminate form

I wrote something for my University's blog. Read til the end! The Unconquered Mathematics of the Inca tmblr.co/Z8P9zkhTcJuq...

I made a new kind of slide rule: 3D-printable! youtu.be/gSthY_v-bLc

There’s a calculus project in here somewhere. Which classical theorems does this demonstrate?

Unwinding an Unusual Slide Rule https://hackaday.com/2025/05/12/unwinding-an-unusual-slide-rule/