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Comment by HPsquared | Hacker News Reader

And 1 nanosecond at light speed ≈ 1 foot

That's remarkably close to reality. I'm impressed :)

    $ units c ft/ns
            * 0.98357106

Admiral Grace Hopper Explains the Nanosecond: https://youtu.be/9eyFDBPk4Yw

The first time I saw one of her demonstrations of a nanosecond, I was confused when she pulled out a length of wire. I don’t remember what class it was in or what context the video was being used, but this was 6th grade

Possibly an urban legend but there's a story about a company in India that ordered a Soviet made computer system that has an sloppy spool of wire attached to the main board. They contacted the Soviet institute that built the computer system and it was explained that the computer needed a timing delay between two components but didn't have the proper ICs on hand so they used a precise length of wire to introduce the needed delay to make the timing correct.

As a stone cold fact physical mediums with known delay timings were once used as memory storage for computers and as "echo removal" filters in radar installations.

    Although a mathematician, Turing took quite an interest in the engineering side of computer design.

    There was some discussion in 1947 as to whether a cheaper substance than mercury could not be found for use as an ultrasonic delay medium.

    Turing's contribution to this discussion was to advocate the use of gin, which he said contained alcohol and water in just the right proportions to give a zero temperature coefficient of propagation velocity at room temperature.

~ MAURICE V. WILKES 1967 A CM Turing Lecture

https://sci-hub.ru/10.1145/321439.321440

https://en.wikipedia.org/wiki/Delay-line_memory

https://www.theregister.com/2013/06/28/wilkes_centenary_merc...

They are still used to test networking equipment under long propagation delays. Spools of fiber hundreds of miles long.

Back in the old days of analog video, component video was three separate cables. When we made custom cables, we had to ensure the cables were the same length to ensure the timing was within tolerance. The day we got to switch to digital SDI which also included audio as like a gift from the gods

This is still a problem for modern multi-lane digital connections, like PCI Express. The solution? Make each individual lane self-timing, and compensate for it digitally in the receiver buffer.

This was probably also due to impedance matching between all the lines involved.

Digital signals (when using N/P balanced lines) also have this problem, to a lesser extent. Some CAD EE design software have ways to design squiggly traces to balanced impedances in traces that have to go around corners on the PCB and end up with different lengths.

There were a lot of delay–line memories back in the day. It wasn’t just that they didn’t have memory chips; memory chips hadn’t been invented yet.

https://www.youtube.com/watch?v=2BIx2x-Q2fE

This is the method used to add delays for HFT to ensure fair(er) markets for all participants on the IEX exchange.

Flash Boys, Michael Lewis

https://en.m.wikipedia.org/wiki/Flash_Boys

GNU units is one of my favorite tools.

kragen's recent HN comment is a gold mine:

<https://news.ycombinator.com/item?id=36988917>

If you like approximations, there is also https://xkcd.com/1047/

my favorite of these not on the xkcd is that there are pretty close to ~5e5 + (5% of 5e5) seconds in 365 24-hour days (a very naive "year")

That's to say, 500000 + 25000 is very nearly 525600. It's only off by ten minutes!

Surely you mean minutes, not seconds. And it's off by 10 hours.

You need bigger feet

And 1 millisecond at the speed of sound ≈ 1 foot as well

Came here to say this. It follows that light is ≈1 million times the speed of sound.

Yeah, I think it would be neat to change time to be defined as 1 chrono = how long it takes for light to go 1e9 meters. 1 kilochrono is 55 minutes. Useful enough for space travel type situations where you can’t rely on solar days for units.

Well, nowadays the meter is defined in terms of the second, so that would be a circular definition. ;)

And second is defined based on specific properties of caesium 133, which doesn't depend on solar time

And the number of seconds in a year is π*10^7, or close enough.

Equivalent but perhaps more catchy: "Pi seconds are a nanocentury".

so to measure a nanocentury you should basically count 3 thousands ... if you want a few more digits of accuracy, count the 3 thousands plus (√2)/10

And 1 googol femtobarns ≈ 1 square teraparsecs

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