Many pendulum clocks are capable of well under 1 ppm accuracy, which is better than many quartz oscillators. Here is a tour of clock precision by orders of magnitude:
> The Shortt was the first clock to be a more accurate timekeeper than the Earth itself; it was used in 1926 to detect tiny seasonal changes in the Earth's rotation rate. Shortt clocks achieved accuracy of around a second per year
That's correct. On NT/Alpha context switching was done in ntos\ke\alpha\ctxsw.s, which was regular kernel mode assembler code. A PAL call was made but it simply set the new Teb and Pdr; two or three lines of code. I've never seen the PALcode for VMS or OSF/Tru64 but the NT PAL for swpctx was designed so that alpha assembler code in NT looked as much like the mips code that davec wrote. It made the port easier that way.
Interesting Raymond continues to mention NT/Alpha now and then. If you run into him mention I have a collection of NT/Alpha artifacts and anecdotes he might be interested in.
That's the price -- when new. But most "time nuts" buy their atomic clocks well used on eBay or local surplus sales at a massive discount. For example the most recent H-maser on the hobbyist market went for just a few thousand. Granted it was in need of repair, but that journey is part of the fun of an atomic timekeeping at home hobby.
Author of the web site (leapsecond.com) here if you have any questions. I don't know how the title of the HN post was chosen. The actual title of the web page is "GPS, UTC, and TAI Clocks".
The page is a javascript animation of "GPS system time", UTC, and TAI showing how they all tick together but are offset from each other by an integer number of seconds. It's a fixed integer in the case of TAI and GPS and a variable integer in the case of UTC.
Leap seconds are an abomination. Anybody who needs astronomical time is not using UTC anyway. If necessary, we could have a leap minute in a century or two.
Google's 24-hour smear makes leap seconds, bad enough already, ever so much worse.
We could fix the problem just by never announcing another one.
TAI and UTC are based on the SI second. The SI second is specifically defined in terms of cesium atoms at no temperature, no velocity, and no elevation (aka, on the geoid). Consequently TAI and UTC are immune from relativistic effects, by definition.
On the other hand, the physical clocks in the laboratory are not immune and that's why they have to be corrected for a dozen factors, the largest of which is usually gravitational redshift. To appreciate the complexity and precision of this correction see this NIST paper:
> TAI and UTC are based on the SI second. The SI second is specifically defined in terms of cesium atoms at no temperature, no velocity, and no elevation (aka, on the geoid). Consequently TAI and UTC are immune from relativistic effects, by definition.
This is not quite correct. The definition of the SI second does not make any requirements or assumptions about the state of motion or location of the cesium atoms. The only requirement is that the device that measures the frequency of the cesium atom hyperfine transition is at rest relative to the atoms themselves and spatially co-located with them. That is what ensures that no relativistic effects are involved in the measurement.
The definitions of TAI and UTC are not simply based on the SI second, but on the SI second as recorded by clocks on the geoid that are at rest relative to the rotating Earth. That extra qualifier is why measurements recorded by clocks not on the geoid have to be adjusted.
I think you might be misunderstanding. Clocks must necessarily have a frame of reference. TAI's frame of reference is imaginary (geoid), and in reality we calculate it from an average.
Because TAI's frame of reference is the geoid it will experience relativistic effects based on earth's motion viewed from any other frame of reference (in OP's example, from the reference of the sun)
Clocks cannot exist without a frame of reference. Accurate timekeeping necessarily involves tracking spatial information as well.
You can grep the web for Dik's original version. The 3-line homage version I linked contains both his full name and the name of the algorithm used: "spigot" (as in spew, faucet), which itself contains the letters PI. In addition, this version outputs exactly 31416 digits of pi. So it's triple self-referential. Happy 2022.03.14 pi day to all.
LF is line feed, thus next line.
The CR
is to
readjust the write head
back to the
starting position.
A line feed alone is not a new line because some or most of the line is already used up. The B '*n' and C '\n' introduced the notion of new line, which outputs both a next line (LF) and back to the starting position (CR).
http://leapsecond.com/ten/
Here is a world record setting pendulum clock from a few years ago:
http://leapsecond.com/pend/clockb/
Precision pendulum clocks are a very deep rabbit hole.