tvb

6 ms·

1.
by tvb 3y ago
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: http://leapsecond.com/ten/ Here is a world record s
2.
by tvb 4y ago
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
3.
by tvb 4y ago
The original volt-nuts mailing list pretty much faded away as the members use the eevblog forum now. See the Metrology section. The time-nuts mailing list is still very active, now in its 23rd year. More info at the group page: http:/
4.
by tvb 4y ago
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 thousan
5.
by tvb 4y ago
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
6.
by tvb 4y ago
> Blockbuster had a chance to buy Netflix in the early 2000's for $50,000,000. Ah, an example of the Butterfly Effect: then we'd have a billion references to FAABG on the web instead of FAANG.
7.
by tvb 4y ago
Previously (and posted 64000/89 days ago): https://news.ycombinator.com/item?id=24929726
8.
by tvb 4y ago
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 d
9.
by tvb 5y ago
The original pi/spigot work was done by Rabinowitz & Wagon [1]. See also the very readable works by Jeremy Gibbons [2] [3]. [1] https://en.wikipedia.org/wiki/Spigot_algorithm [2] https://www.cs.ox.a
10.
by tvb 5y ago
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 addit
11.
by tvb 5y ago
With a nod to fellow pi-hound Dik T Winter, three equal lines of C give 32k digits of pi: http://leapsecond.com/tools/pi3.c
12.
by tvb 5y ago
> LF is line feed, thus new line. LF is line feed, thus next line. The CR is to readjust the write head back to the starting position. A line feed
13.
by tvb 5y ago
Only a positive leap second is “over in a second”. A negative leap second is essentially “over before it starts”. This asymmetry is an opportunity for code to implement UTC incorrectly. Another issue is that a positive leap second cannot be
14.
by tvb 5y ago
DCF77 has a leap second warning bit. PTB says it is up to the user to know if it positive or negative. If a clock blindly assumes it is a positive leap that’s an error in the design of the clock. This is not ideal. Likewise WWVB has a leap
15.
by tvb 5y ago
True, but note the GPS data transmission rate is only 50 bps; yes, just 50 bits per second. The signal is so week and so slow that after headers and error correction you get less than 4 bytes of data per second. When comparing satellite r
16.
by tvb 5y ago
Don't worry. This happened once before in 2003 [1]. UTC has provisions for positive or negative leap seconds; that works fine. GPS runs without the hassle of leap seconds; that works fine too. GPS users often want to know UTC, so GPS a
17.
by tvb 6y ago
As a patient hobbyist collector I try to buy one of each. My goal was to learn the history and theory of each one, explore the magnificent design, measure the actual timing accuracy, read as many old books or articles about them, and in som
18.
by tvb 6y ago
Yes, 500 pounds of gear sounds about right. I was aware that the car was slightly heavier than usual and drove accordingly. There was no hurry; it was not a race, just a leisurely weekend trip, about 2.5 hours in the car, with an average sp
19.
by tvb 6y ago
Look for any vintage caesium clock made by National, Varian, Hewlett-Packard / Agilent / Symmetricom / Microsemi / Microchip, FEI, FTS / Austron / DATUM, Oscilloquartz, and maybe others. None of them are a rest
20.
by tvb 6y ago
I anticipated that, so I had relativity books and physics magazines with pictures of Einstein on the front seat just in case we got stopped and the officer wanted a quick lesson in the fun of measuring time dilation. It was 2005, the 50th a
21.
by tvb 6y ago
If you have experience with analog and digital electronics it's not very hard. Atomic clocks were part of Hewlett-Packard's glory days and in that era the user got full documentation, schematics, theory, trouble-shooting guides, e
22.
by tvb 6y ago
Cesium atomic clocks are not radioactive, nor are they based on radioactive decay. The isotope used for cesium beam atomic clocks is natural and stable Cs-133. The clock is based on an ultra-precise energy transition near 9.192 GHz. You may
23.
by tvb 6y ago
Yes, the original Mt Rainier experiment in 2005 caught the attention of Stephen Hawking and I was asked to repeat the experiment for his PBS/BBC TV series in 2016. It was mid-winter up here in PNW so we used Mt Lemmon in Arizona instea
24.
by tvb 6y ago
Thanks, DanG. Author here. I happen to be reading HN right now if anyone has questions about cesium clocks or using them to demonstrate relativistic effects. This is just a DIY hobby of mine.
25.
by tvb 6y ago
About 70 lbs (30 kg), so not difficult to lift or carry with two hands. But it took a real man (my brother-in-law, construction worker) to hold it outstretched like you see in the photo.
26.
by tvb 6y ago
Cesium beam atomic clocks are available on the surplus market, though not nearly as common or as cheap as Rubidium. The clock in the photo is model hp 5071A and I got it on eBay 20 years ago. The tube will last on the order of 7 to 20 years
27.
by tvb 11y ago
One degree is 40,000 km / 360 = 111 km at the equator. But Greenwich is at 51 degrees latitude so you apply a cos (51.5°) = 0.622 factor. That's why 1 degree of longitude at latitude 51 is 69 km. Does that help clear it up? Note a
28.
by tvb 11y ago
Makes a good C interview question: char c; short h; int i; char *s; 1 = sizeof (char) 2 = sizeof (short) 4 = sizeof (int) 4 = sizeof (float) 8 = sizeof (double) 1 = sizeof (c) 2 = sizeof (h)