Author Topic: Forum Timestamps Inconsistent with Other Accounts of Events  (Read 8825 times)

Offline ChrisWilson68

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Re: Forum Timestamps Inconsistent with Other Accounts of Events
« Reply #20 on: 07/23/2020 09:26 pm »
My bet is that the site has a single time that it does the time change from standard to DST. Perhaps the site uses the last Sunday of March as many European countries do. Since Boca Chica changed its time on the second Sunday of March as the US does, leaping ahead one hour, this would make sense of the discrepancy. In Boca Chica the time was an hour ahead because it had changed to DST already but the site hadn't realized the change.
That's consistent with a quick look at the underlying forum code -- it uses the system's default DST transition rules and then adds in your offset from GMT, rather than trying to use a client-dependent, client-supplied set of rules for DST transition.

What's odd is that if I add "%Z" (timezone name) and "%s" (UNIX/POSIX timestamp in decimal) to the Time Format string in the Profile, it displays "BST" as a timezone but displays times consistent with UTC/GMT:
Current forum time: 2020-07-23, 20:55:27 (BST: 1595537727)

while on my end if I ask for London time I get:
TZ=Europe/London date +"%Y-%m-%d, %H:%M:%S (%Z: %s)"
2020-07-23, 21:56:55 (BST: 1595537815)

which is British Summer Time (UTC+1)

I think that's because it uses the offset you have set in your profile as a hack on top of using Europe/London for timezone information.

A nice fix for this would be to allow an Olsen time zone name (such as Europe/London or America/Los_Angeles) to be selected in the user profile rather than a numeric offset from UTC.

Offline launchwatcher

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Re: Forum Timestamps Inconsistent with Other Accounts of Events
« Reply #21 on: 07/23/2020 09:35 pm »
My bet is that the site has a single time that it does the time change from standard to DST. Perhaps the site uses the last Sunday of March as many European countries do. Since Boca Chica changed its time on the second Sunday of March as the US does, leaping ahead one hour, this would make sense of the discrepancy. In Boca Chica the time was an hour ahead because it had changed to DST already but the site hadn't realized the change.
That's consistent with a quick look at the underlying forum code -- it uses the system's default DST transition rules and then adds in your offset from GMT, rather than trying to use a client-dependent, client-supplied set of rules for DST transition.

What's odd is that if I add "%Z" (timezone name) and "%s" (UNIX/POSIX timestamp in decimal) to the Time Format string in the Profile, it displays "BST" as a timezone but displays times consistent with UTC/GMT:
Current forum time: 2020-07-23, 20:55:27 (BST: 1595537727)

while on my end if I ask for London time I get:
TZ=Europe/London date +"%Y-%m-%d, %H:%M:%S (%Z: %s)"
2020-07-23, 21:56:55 (BST: 1595537815)

which is British Summer Time (UTC+1)

I think that's because it uses the offset you have set in your profile as a hack on top of using Europe/London for timezone information.

No, that's from the "Current Forum Time" displayed on the profile page which does not include the time offset - it shows a UTC timestamp rather than my local time.

Offline ThreadSnake

My bet is that the site has a single time that it does the time change from standard to DST. Perhaps the site uses the last Sunday of March as many European countries do. Since Boca Chica changed its time on the second Sunday of March as the US does, leaping ahead one hour, this would make sense of the discrepancy. In Boca Chica the time was an hour ahead because it had changed to DST already but the site hadn't realized the change.
That's consistent with a quick look at the underlying forum code -- it uses the system's default DST transition rules and then adds in your offset from GMT, rather than trying to use a client-dependent, client-supplied set of rules for DST transition.

What's odd is that if I add "%Z" (timezone name) and "%s" (UNIX/POSIX timestamp in decimal) to the Time Format string in the Profile, it displays "BST" as a timezone but displays times consistent with UTC/GMT:
Current forum time: 2020-07-23, 20:55:27 (BST: 1595537727)

while on my end if I ask for London time I get:
TZ=Europe/London date +"%Y-%m-%d, %H:%M:%S (%Z: %s)"
2020-07-23, 21:56:55 (BST: 1595537815)

which is British Summer Time (UTC+1)

Thanks for taking a look at what it's doing in the code! I didn't know where to go to get the code before your post.

My looking through forum posts, going into the beginning of April, times began to be accurate, aligning with British Time's Daylight Savings Time beginning.
Hello, I gather and organize Starship development data.
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Offline ThreadSnake

I've seen that the time on posts are accurate when British Daylight Savings is active.

When it starts:

1 Hour Behind:
https://forum.nasaspaceflight.com/index.php?topic=47120.msg1928296#msg1928296

On time:
https://forum.nasaspaceflight.com/index.php?topic=47120.msg1929468#msg1929468


And when it ends:

On time:
https://forum.nasaspaceflight.com/index.php?topic=48895.msg2008158#msg2008158

1 Hour Behind:
https://forum.nasaspaceflight.com/index.php?topic=48895.msg2009195#msg2009195

Definite Correlation here.

The fact that the times are 1 hour behind when British DST isn't active, makes me wonder if in northern winter when DST isn't active, if the forum posts from when it is active will be 1 hour ahead or not. That is my hunch for now. (If that makes sense and if someone can confirm that theory or disprove it, that would be welcome)
« Last Edit: 07/24/2020 05:42 pm by ThreadSnake »
Hello, I gather and organize Starship development data.
[email protected]:01 UTC - Timeline Updates, [email protected]:01 UTC: RGV pic parts census.

Offline Llian Rhydderch

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Re: Forum Timestamps Inconsistent with Other Accounts of Events
« Reply #24 on: 07/24/2020 05:59 pm »
Idea:  why don't we do on NSF the same thing as we do on all spaceflight, human and satellite:  use UTC.  Gives one time stamp for all spaceflight related events, for everyone around the globe.

When local times matter, like local launches from Florida or Guiana or Satish Dhawan, it would make only a single adjustment to UTC rather than the multiple ones required to get times from two local timezones synced up, given disparate political daylight savings rulz, etc.



« Last Edit: 07/24/2020 06:00 pm by Llian Rhydderch »
Re arguments from authority on NSF:  "no one is exempt from error, and errors of authority are usually the worst kind.  Taking your word for things without question is no different than a bracket design not being tested because the designer was an old hand."
"You would actually save yourself time and effort if you were to use evidence and logic to make your points instead of wrapping yourself in the royal mantle of authority.  The approach only works on sheep, not inquisitive, intelligent people."

Offline ChrisWilson68

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Re: Forum Timestamps Inconsistent with Other Accounts of Events
« Reply #25 on: 07/24/2020 06:10 pm »
Idea:  why don't we do on NSF the same thing as we do on all spaceflight, human and satellite:  use UTC.  Gives one time stamp for all spaceflight related events, for everyone around the globe.

When local times matter, like local launches from Florida or Guiana or Satish Dhawan, it would make only a single adjustment to UTC rather than the multiple ones required to get times from two local timezones synced up, given disparate political daylight savings rulz, etc.

I vote against that.  In my daily life, I use my local time zone.  So does nearly every human on Earth.  Virtually every web site supports that.  Virtually every piece of electronic equipment.  Virtually every piece of software.  It would be inconvenient for me to have to see all the timestamps on this site in UTC and try to mentally translate that into the local time which I use for the rest of my life.

This is an obscure bug that makes the timestamps of old posts in a window for a few weeks in March show a timestamp that's off by an hour.  That's far less of a pain than having to mentally translate UTC all the time.

Offline ChrisWilson68

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Re: Forum Timestamps Inconsistent with Other Accounts of Events
« Reply #26 on: 07/24/2020 06:15 pm »
If this site just let us choose an Olsen time zone name in our profile and used that correctly, then anyone who wanted to see UTC could choose to see it and anyone who wanted to see any other time zone could see that.

From what people on here have said, the server software for this site is actually calling library routines that can handle any Olsen time zone correctly.  It's just not choosing to let the user set an Olsen name and passing that through to these routines.  Instead, it's using the system time zone of the server and hacking on an offset of a number of hours different from UTC.  This could be changed.

Offline Ken the Bin

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Re: Forum Timestamps Inconsistent with Other Accounts of Events
« Reply #27 on: 07/24/2020 11:24 pm »
I've found that the simplest thing to do is when the timestamps on posts are not correct is to go to Profile > Modify Profile > Look and Layout.  Then I click "(auto detect)" next to the Time Offset and it gets changed to the needed value to make the timestamps correct.

I find that I need to do this more than just twice/year.

Offline ChrisWilson68

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Re: Forum Timestamps Inconsistent with Other Accounts of Events
« Reply #28 on: 07/24/2020 11:32 pm »
I've found that the simplest thing to do is when the timestamps on posts are not correct is to go to Profile > Modify Profile > Look and Layout.  Then I click "(auto detect)" next to the Time Offset and it gets changed to the needed value to make the timestamps correct.

I find that I need to do this more than just twice/year.

The issue isn't with the time for current posts.  That can be fixed by changing the time offset value.

The issue is that if you're in the US then when you look at old posts from the middle of March the timestamps are one hour off while the posts for the rest of the year have correct timestamps.  Those in timezones whose daylight savings time changes are the same as the UK's will not see this issue.  The same is presumably true for posts from a few weeks in the fall between the end of Summer Time in the UK and the end of Daylight Savings Time in the US.

Offline Ken the Bin

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Re: Forum Timestamps Inconsistent with Other Accounts of Events
« Reply #29 on: 07/24/2020 11:49 pm »
The issue is that if you're in the US then when you look at old posts from the middle of March the timestamps are one hour off while the posts for the rest of the year have correct timestamps.  Those in timezones whose daylight savings time changes are the same as the UK's will not see this issue.  The same is presumably true for posts from a few weeks in the fall between the end of Summer Time in the UK and the end of Daylight Savings Time in the US.

Interesting.  I've never noticed that, and I am in a US time zone that observes DST.

Having both the server and the database values in UTC seems to be the best option.

Offline ThreadSnake

I've found that the simplest thing to do is when the timestamps on posts are not correct is to go to Profile > Modify Profile > Look and Layout.  Then I click "(auto detect)" next to the Time Offset and it gets changed to the needed value to make the timestamps correct.

I find that I need to do this more than just twice/year.

The issue isn't with the time for current posts.  That can be fixed by changing the time offset value.

The issue is that if you're in the US then when you look at old posts from the middle of March the timestamps are one hour off while the posts for the rest of the year have correct timestamps.  Those in timezones whose daylight savings time changes are the same as the UK's will not see this issue.  The same is presumably true for posts from a few weeks in the fall between the end of Summer Time in the UK and the end of Daylight Savings Time in the US.

The period of innacuraccy isn't just in March. It's any time that British Daylight Savings time is not in affect.
Hello, I gather and organize Starship development data.
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Offline ChrisWilson68

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Re: Forum Timestamps Inconsistent with Other Accounts of Events
« Reply #31 on: 07/25/2020 03:30 pm »
I've found that the simplest thing to do is when the timestamps on posts are not correct is to go to Profile > Modify Profile > Look and Layout.  Then I click "(auto detect)" next to the Time Offset and it gets changed to the needed value to make the timestamps correct.

I find that I need to do this more than just twice/year.

The issue isn't with the time for current posts.  That can be fixed by changing the time offset value.

The issue is that if you're in the US then when you look at old posts from the middle of March the timestamps are one hour off while the posts for the rest of the year have correct timestamps.  Those in timezones whose daylight savings time changes are the same as the UK's will not see this issue.  The same is presumably true for posts from a few weeks in the fall between the end of Summer Time in the UK and the end of Daylight Savings Time in the US.

The period of innacuraccy isn't just in March. It's any time that British Daylight Savings time is not in affect.

Can you point to a post that shows that there is a problem on a date when neither the UK nor the US is observing daylight savings?

Offline Hog

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Re: Forum Timestamps Inconsistent with Other Accounts of Events
« Reply #32 on: 07/25/2020 04:39 pm »
I've always noticed a weirdo bug that affects the resultant time on this site.  Many time zones in the United States and in Canada are shared.  Not sure about Mexico though. 
I live in a timezone that "celebrates" either EST(Eastern Standard Time) or EDT(Eastern Daylight Time).  EST is 5 hours behind and EDT is 4 hours behind the UTC(Universal Time Coordinated/Universal Coordinated Time).  UTC is also known as GMT for Greenwich Mean Time, as the geographical Prime Meridian, where all Earth time zones originate from, passes through the Royal Observatory, Greenwich, London, England in the UK.
I do suggest reading a bit about GMT as some context must be given if trying to compare GMT directly to UTC. Interesting stuff.
Wiki page GMT https://en.wikipedia.org/wiki/Greenwich_Mean_Time

Corporal: "Private, get up its your turn for "fire picket"."
Me: "What time is it?"
Corporal: "Time for you to get your butt out of bed, into uniform and outside for fire picket."

Fire picket is where a service member wakes up, dresses and walks around an assigned area looking for fire. After his/her usually one-hour "fire picket", you awaken the next member and they get up, walk around and search for fire for the next hour.  Fire picket is a normal part of certain military life.  The reason why I didnt like it was because it was often used as a form of punishment. There was one day during morning inspection, while standing at attention, Sergeant Rodgers was in my face and he caused me to laugh.  He gave me a few chances to correct myself, but I was unable.
He said "Private S-alphabet-horn" we'll see how much you're laughing tomorrow morning after a night of fire picket."
Usually that means 2 sessions of fire picket. And one of them is almost always either the first hour of fire picket, or the last hour before reveille. Either one of these time slots allows you to either stay in uniform or get into uniform an hour early before you start your normal day.  Well I lucked out and saw that I had both the first AND the last shifts for fire picket which would give me a nice 4 hour solid block of time for sleeping, but unluckily I noticed that I had been scheduled for  THREE hours of fire picket. I hour is normal, 2 hours is punishment, 3 hours means that you really PO'ed someone.

2300-lights out
2300-2400 Shift #1
0000-0100 off
0100-0200-off
0200-0300 Shift #2
0300-0400-off
0400-0500 Shift #3
0500-reveille

So as you can see that at midnight I had 2 hours to remove my boots/uniform/sleep/awake/redress, fire picket at 0200-0300 then 1 hour to remove my boots/uniform/sleep/awake/redress for an 0400-0500 fire picket.

During the next mornings morning inspection Sergeant Rodgers steps in front of me, right in my face, I can see all the hairwax gobbed into his moustache holding his moustache up into these gigantic handlebars in order to keep his moustache "within regulations" and says "Private S-alphabet-horn, somethings different today" and pauses and puts a finger up to his ear in the dead silent room.  "I don't hear any laughing." with a big manure eating grin on his face. He said "Have a great day Private." and moves on to the next soldier.

He was right, no I wasn't laughing, and I never forgot that day, nor his name some decades later.  BTW At the end of that course,  I was outside alone having a cigarette. Sgt. Rodgers walked up to me, lit his cigarette.  He said "Every so often I see a Private that has that "special something" that will make them an excellent Sergeant in the future.   You Private Schermerhorn, have that "special something"."  With that he reaches into his pocket and pulls out an extra set of his Sergeant chevrons(3 chevrons with a Maple Leaf above them and places them into my hands.  "I don't want to hear about you wearing these around base, but maybe they will remind you that I noticed the good part of your efforts, and not just the bad."  He then shakes my hands and walks away.  Wow, such a simple gesture made such a HUGE impression on me. I'll never forget it.
« Last Edit: 07/25/2020 04:41 pm by Hog »
Paul

Offline ChrisWilson68

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Re: Forum Timestamps Inconsistent with Other Accounts of Events
« Reply #33 on: 07/25/2020 05:00 pm »
UTC is also known as GMT for Greenwich Mean Time

Actually, no.  GMT and UTC are close, but they are not the same thing.

As the first and second paragraphs of the Wikipedia article on GMT you linked to say:

Quote
At different times in the past, it has been calculated in different ways, including being calculated from noon;[1] as a consequence, it cannot be used to specify a precise time unless a context is given.

English speakers often use GMT as a synonym for Coordinated Universal Time (UTC).[2] For navigation, it is considered equivalent to UT1 (the modern form of mean solar time at 0 longitude); but this meaning can differ from UTC by up to 0.9 s. The term GMT should not thus be used for certain technical purposes requiring precision.

GMT is based on the rotation of the Earth.  That speeds up and slows down very slightly over time.  It gives variable day lengths.

That's why people came up wtih UTC, as something better to use than GMT.  All modern timezones are based on offsets from UTC, not GMT.

UTC is based on seconds of a fixed length defined independent of the variable rotation of the Earth.  It is close to UT1, a time that is based on the rotation of the Earth and essentially a better-defined version of GMT.  When the variable rotation of the Earth starts bringing UTC close to being 1 second away from UT1, a leap second is either added or removed from UTC to keep it close to UT1.  This leap second system to keep UTC in sync with solar days is really not much different in principle from leap years which are used to keep the Gregorian calendar in synch with solar years.

Anyway, what all this means in terms of terminology is that we should really be using the terms UTC or "coordinated universal time" when that's what we mean, not GMT.  UTC is what all timezones are based on and what computers actually use (as closely as they can) for virtually all purposes.

Offline Hog

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Re: Forum Timestamps Inconsistent with Other Accounts of Events
« Reply #34 on: 07/26/2020 02:06 pm »
You are technically correct of course, GMT and UTC are NOT the same thing.

In an attempt to reduce the population of nits, I included this sentence "I do suggest reading a bit about GMT as some context must be given if trying to compare GMT directly to UTC. Interesting stuff."   
Nits are pesky insects though.
Maybe I should have asked Sgt Rodgers if his fire picket schedule was following UTC or GMT? 
(from ZULU (UTC) is the correct answer)
Paul

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