General > General Technical Chat
DateTime: as usual Randall Monroe is clued up
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tggzzz:
This will be appreciated by everyone that has had to explain to someone why dates and times are recursively more difficult than most people "think" (and I use that word loosely).

Don't believe me? Start by asking them how many seconds there are in a minute, how many hours there are in a day, and how many months there are in a year.  I didn't realise the relatavistic differences, and I'm not sure how I could observe them :)

The caption is "It's not just time zones and leap seconds. SI seconds on Earth are slower because of relativity, so there are time standards for space stuff (TCB, TGC) that use faster SI seconds than UTC/Unix time. T2 - T1 = [God doesn't know and the Devil isn't telling.]"

nctnico:
Not just for space. Data in fiber optic connections has different speeds depending on whether the signal travels with the earth's rotation or against it. For some systems this matters enough that it needs to be compensated for.

In general I loath dealing with date & time in software but somehow I ended up involved with the highest end large scale time&frequency distribution systems.
coppice:
I used to take recordings of sensor data recorded on aircraft, and run them through simulations of back end systems at a fraction of real time - typically 1/8th, 1/16th or 1/32nd, depending how fast we could make our simulation. So, the concept of "real time" became vague. Was real time the sensor recording domain, or our replay domain? We settled on jargon based on the movie "This Island Earth". "10 our our Earth minutes" became time on the clock in the room, while "10 minutes of real time" became 10 minutes on the aircraft. Get your jargon right, and you are good to go. :)
tggzzz:

--- Quote from: coppice on December 14, 2023, 11:58:29 am ---I used to take recordings of sensor data recorded on aircraft, and run them through simulations of back end systems at a fraction of real time - typically 1/8th, 1/16th or 1/32nd, depending how fast we could make our simulation. So, the concept of "real time" became vague. Was real time the sensor recording domain, or our replay domain? We settled on jargon based on the movie "This Island Earth". "10 our our Earth minutes" became time on the clock in the room, while "10 minutes of real time" became 10 minutes on the aircraft. Get your jargon right, and you are good to go. :)

--- End quote ---

Get your jargon right, and the next subtle "issue" will reveal itself :( Recursively :( :(
tggzzz:

--- Quote from: nctnico on December 14, 2023, 11:45:55 am ---Not just for space. Data in fiber optic connections has different speeds depending on whether the signal travels with the earth's rotation or against it. For some systems this matters enough that it needs to be compensated for.

--- End quote ---

And for some applications the speed of light in optical fibres is too slow. Hence the High Frequency Trading mob buying up the microwave towers between Chicago and New York, to save a few milliseconds propagation delay. But that mob also encode trading business rules in FPGA hardware, to keep latency low.

For example...
In terms of niche jobs for developers in the financial services industry, it’s hard to get more niche than roles for engineers who work on ultra-ultra low latency systems at systematic hedge funds and high speed market making firms. They don’t come up often, and when they do, they require a special talent: the ability to program field-programmable gate arrays (FPGAs). Both quantitative hedge funds and high speed market making firms hire FPGA engineers. In finance, they’re found everywhere from Citadel Securities, to DE Shaw, Susquehanna International, Maven Securities and Jump Trading. Few come from a financial services background: most are drawn from chip design and hardware engineering firms. Ben Hodzic, executive director specializing in quantitative analytics at recruitment firm Selby Jennings in New York, says they can be hard to come by: there simply aren’t that many FPGA programmers to go around. “Most trading firms will consider FPGA talent from out of industry, given how hard they are to find and how niche of a skill set it is.”
https://www.efinancialcareers.com/news/2021/07/fpga-engineer-salaries-hedge-funds-market-makers
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