keelbolt
Well-Known Member
Time has come to replace my old quartz watch. Does anyone have any recommendations for a good quartz watch that will keep good time for use with Astro?
KB
KB
Good quartz watch for Astro?
- Thread starter keelbolt
- Start date
beneteau_305_553
Well-Known Member
http://www.casio.co.uk/Products/Watches/Wave%20Ceptor/WVA-210DU-1AVER/At%20a%20Glance/
On offer in sunday times for £70
On offer in sunday times for £70
MASH
N/A
Surely a quartz watch isn't enough for astro? I thought you needed a chronometer.
whipper_snapper
Well-Known Member
That is a radio controlled watch which is not much use out of range of the transmitters.
I wold suggest a cheapo digital - they are plenty accurate enough for astro with occasional resetting via a time signal.
I wold suggest a cheapo digital - they are plenty accurate enough for astro with occasional resetting via a time signal.
D
Deleted member 478
Guest
As long as you know how much time it gains or loses per day, it will be fine.
TigaWave
Well-Known Member
The cheapest Casio is fine for astro, if you have a radio receiver you can check the time every day. In practice they will be more than good enough for the accuracy of your sights.
A
Anonymous
Guest
A GPS gives the most accurate time signal available. It's pretty useful for giving you a position, too /forums/images/graemlins/tongue.gif
Talbot
Well-Known Member
Recomendation is that buying 3 cheaper Quartz watches and retaining them in a decent shock proof mounting will provide the best compromise for astro. You need to then compare them against the time check available over the internet, and I dont have the reference for that here. You then need to calibrate all three and retain records, thus you can get an accurate time by comparison of their differences and their calibration.
GPS is not the most accurate time - this used to be sent over HF (and may still be) but is also sent over the internet from USA. besides the whole point of astro is to be able to use it if GPS is unavailable.
GPS is not the most accurate time - this used to be sent over HF (and may still be) but is also sent over the internet from USA. besides the whole point of astro is to be able to use it if GPS is unavailable.
A
Anonymous
Guest
[ QUOTE ]
GPS is not the most accurate time ....
[/ QUOTE ] http://www.ntp-time-server.com/gps-time-server/gps-time-server.htm "The accuracy of time signals from GPS is limited to ±340 nanoseconds (where 1 nanosecond = 0.000 000 001 seconds) by a deliberate distortion of the satellite signal (for military security) called Selective Availability. "
Not the most accurate time? What is more accurate than that - in any available or usable form? As for GPS not being available, I was being a bit ironic and tongue in cheek but honestly, does anyone use astro on the real assumption that GPS will go down? You'd better keep all your money in gold sovereigns, etc. I keep a Seafix RDF in the side locker and would use that in dire emergency but I have quite a lot of GPS sources on board including a handheld - I guess most people do, these days?
Still, I'm not knocking astro, it is all good stuff and back to basics. Shame more people don't take an interest in it and good than many do.
GPS is not the most accurate time ....
[/ QUOTE ] http://www.ntp-time-server.com/gps-time-server/gps-time-server.htm "The accuracy of time signals from GPS is limited to ±340 nanoseconds (where 1 nanosecond = 0.000 000 001 seconds) by a deliberate distortion of the satellite signal (for military security) called Selective Availability. "
Not the most accurate time? What is more accurate than that - in any available or usable form? As for GPS not being available, I was being a bit ironic and tongue in cheek but honestly, does anyone use astro on the real assumption that GPS will go down? You'd better keep all your money in gold sovereigns, etc. I keep a Seafix RDF in the side locker and would use that in dire emergency but I have quite a lot of GPS sources on board including a handheld - I guess most people do, these days?
Still, I'm not knocking astro, it is all good stuff and back to basics. Shame more people don't take an interest in it and good than many do.
TigaWave
Well-Known Member
gps failing?...I've had three fail within 6 hours of each other, so I keep up my astro practice and have a couple of watches...old rdf gave up many years ago! but the sextant is still working.
keelbolt
Well-Known Member
Thanks, guys. Will get a couple of cheap digitals, and monitor their gain/ loss per day for a while.
All helpful stuff. Agree totally about asto - am going to try the Navigator Programme on the laptop this next trip just for fun.
KB
All helpful stuff. Agree totally about asto - am going to try the Navigator Programme on the laptop this next trip just for fun.
KB
Blueboatman
Well-Known Member
Talbot is absolutely right.
I used 2 £10 casios(3 would be better) and did not take them out of their shop wrappers.
It is also quite useful to carry a spare plastic sextant or two as well-you can always sell them off easily later (as I did) .
With this set up and a decent windvane,you need have no fear of flat betteries or total electrical failure whilst voyaging,smart thinking.
I used 2 £10 casios(3 would be better) and did not take them out of their shop wrappers.
It is also quite useful to carry a spare plastic sextant or two as well-you can always sell them off easily later (as I did) .
With this set up and a decent windvane,you need have no fear of flat betteries or total electrical failure whilst voyaging,smart thinking.
beneteau_305_553
Well-Known Member
The instruction manual that comes with the Davis mk 15 is very good. Easy to understand and makes astro navigation easy to use.
whipper_snapper
Well-Known Member
I feel doubly lakesailored!
jimbaerselman
Well-Known Member
[ QUOTE ]
gps failing?...I've had three fail within 6 hours of each other
[/ QUOTE ]
They're meant to run on 6v dc, not 240v ac /forums/images/graemlins/wink.gif
gps failing?...I've had three fail within 6 hours of each other
[/ QUOTE ]
They're meant to run on 6v dc, not 240v ac /forums/images/graemlins/wink.gif
Talbot
Well-Known Member
You obviously dont understand GPS or how it works.
Selective availability is a wobbling of the time reference in the signal from satellite to ground in order to decrease the accuracy of the position. At the moment that aspect is not switched on.
It does not affect the clock accuracy.
However the clock accuracy of GPS is not to the same standard as the world clocks and gets increasingly inaccurate. Therefore, there is a device to bring them back into line called a leap second. The difference between Coordinated Universal Time UTC and the International Atomic Time TAI is :
from 2006 January 1, 0h UTC, until further notice : UTC-TAI = -33 s
Leap seconds can be introduced in UTC at the end of the months of December
or June, depending on the evolution of UT1-TAI. Bulletin C is mailed every
six months, either to announce a time step in UTC, or to confirm that there
will be no time step at the next possible date. - Quote from Earth Orientation Center of IERS, Observatoire de Paris, France.
Selective availability is a wobbling of the time reference in the signal from satellite to ground in order to decrease the accuracy of the position. At the moment that aspect is not switched on.
It does not affect the clock accuracy.
However the clock accuracy of GPS is not to the same standard as the world clocks and gets increasingly inaccurate. Therefore, there is a device to bring them back into line called a leap second. The difference between Coordinated Universal Time UTC and the International Atomic Time TAI is :
from 2006 January 1, 0h UTC, until further notice : UTC-TAI = -33 s
Leap seconds can be introduced in UTC at the end of the months of December
or June, depending on the evolution of UT1-TAI. Bulletin C is mailed every
six months, either to announce a time step in UTC, or to confirm that there
will be no time step at the next possible date. - Quote from Earth Orientation Center of IERS, Observatoire de Paris, France.
A
Anonymous
Guest
[ QUOTE ]
You obviously dont understand GPS or how it works.
[/ QUOTE ]Tell that to the website that published the information - I posted the link and the paragraph. According to that website they do fiddle with the clock. Don't know, but please read the article; they are talking about nanoseconds - what difference is a few nanoseconds going to make to your astro?
/forums/images/graemlins/laugh.gif
You obviously dont understand GPS or how it works.
[/ QUOTE ]Tell that to the website that published the information - I posted the link and the paragraph. According to that website they do fiddle with the clock. Don't know, but please read the article; they are talking about nanoseconds - what difference is a few nanoseconds going to make to your astro?
/forums/images/graemlins/laugh.gif
Talbot
Well-Known Member
Try reading my response again. The nano second wobble is on the position. The difference between Atomic clock time and the GPS time is measured in seconds, The GPS time is synchronised between the satellites to ensure the full accuracy, and only wobbled when transmitted for selective availability, however, they also transmit he correct accurate signal at the same time for the military, and I suspect that every receiver uses that for GPS time, but it is still not synchronised with the world atomic clocks, such that every so often they have to introduce leap seconds to correct the GPS clocks.
Now when I do astro, I like to get as accurate as possible, and a clock error of several seconds is not going to help.
However if you know better - so be it
/forums/images/graemlins/smirk.gif
Now when I do astro, I like to get as accurate as possible, and a clock error of several seconds is not going to help.
However if you know better - so be it
/forums/images/graemlins/smirk.gif
A
Anonymous
Guest
First two apologies - I didn't mean for my smiley to become that ridiculous animated gif - must have seemed a bit rude, and not intended. And, when I answered your post half of it was missing and I did not read the part where you explained about UTC.
Anyway, apart from that, I am still very surprised if you are right on this. Selective Availability is a red herring when it comes to the absolute accuracy of the time signal for manual timing such as astro sights. We are certainly talking about nanoseconds of degradation. As for the fundamental difference with UTC I have been unable to get a completely unambiguous answer but I cannot believe your figure of 33 seconds. I have found a figure of 0.9 seconds but I am not happy that's the correct answer either. When I looked at this a couple of years ago I got a figure, from NPL I think, of far less than 0.1 second which is the shortest interval that a human could ever be interested in for readings.
I will try to get a credible source and get back to you...unless someone else can post a credible link meanwhile.
Regards, David
Anyway, apart from that, I am still very surprised if you are right on this. Selective Availability is a red herring when it comes to the absolute accuracy of the time signal for manual timing such as astro sights. We are certainly talking about nanoseconds of degradation. As for the fundamental difference with UTC I have been unable to get a completely unambiguous answer but I cannot believe your figure of 33 seconds. I have found a figure of 0.9 seconds but I am not happy that's the correct answer either. When I looked at this a couple of years ago I got a figure, from NPL I think, of far less than 0.1 second which is the shortest interval that a human could ever be interested in for readings.
I will try to get a credible source and get back to you...unless someone else can post a credible link meanwhile.
Regards, David
A
Anonymous
Guest
OK, this is very badly written but I think it addresses all the confusions. The conclusion is that the time shown on your GPS is within nanoseconds of the correct UTC but this is derived from a GPS time that is known to be 'out' by a known amount and corrected. All GPS manufacturers use the correction, it seems. Please look at the whole link but especially the following excerpt:-
http://gpsinformation.net/main/gpstime.htm
Because of this process, GPS cannot tolerate the introduction of leap seconds. Hence, in 1980, when the Department of Defense started keeping time on the GPS satellites, its system time and frequency were set to agree with UTC(USNO MC). At that time, TAI minus UTC was 19 seconds. Since then, UTC has been delayed many leap seconds and GPS time has not. Hence, GPS time is still very close to TAI minus 19 seconds. The
specification on GPS time is that it is to be kept within one microsecond of UTC(USNO MC) modulo one second. In other words, as a leap second is introduced into UTC(USNO MC) time, no such step occurs in GPS time. But GPS time is still steered to agree as well as possible with UTC(USNO MC), as if no leap seconds had occurred since 1980. In practice, the steering performance is much better than the one-microsecond specification; typically, it is well within 40 nanoseconds.
In order to provide an estimate of UTC time derivable from a GPS signal, a set of UTC corrections is also provided as part of the broadcast signal. This broadcast message includes the time difference in whole seconds between GPS time and UTC. During 1996 GPS time minus UTC time was 11 seconds. Also included in this message is the rate and time difference estimate between GPS time and UTC(USNO MC) modulo one second. This allows a receiver, in principle, to calculate an accurate estimate of UTC(USNO MC). The mission goal is 28 ns (1 sigma). Outside of the purposeful current degradation of the GPS signal (called Selective Availability, SA) by the DoD for security purposes, this calculation may have an accuracy of about 10 nanoseconds (ns) on an rms basis. Since USNO has been successful in predicting UTC to within about 10 ns, combining these two independent error sources yields a real-time potential uncertainty for UTC available from GPS at about the 14-ns level. In practice, SA prohibits achieving this accuracy level unless special clock systems and filtering techniques are employed. The SA degradation can be filtered away.
http://gpsinformation.net/main/gpstime.htm
Because of this process, GPS cannot tolerate the introduction of leap seconds. Hence, in 1980, when the Department of Defense started keeping time on the GPS satellites, its system time and frequency were set to agree with UTC(USNO MC). At that time, TAI minus UTC was 19 seconds. Since then, UTC has been delayed many leap seconds and GPS time has not. Hence, GPS time is still very close to TAI minus 19 seconds. The
specification on GPS time is that it is to be kept within one microsecond of UTC(USNO MC) modulo one second. In other words, as a leap second is introduced into UTC(USNO MC) time, no such step occurs in GPS time. But GPS time is still steered to agree as well as possible with UTC(USNO MC), as if no leap seconds had occurred since 1980. In practice, the steering performance is much better than the one-microsecond specification; typically, it is well within 40 nanoseconds.
In order to provide an estimate of UTC time derivable from a GPS signal, a set of UTC corrections is also provided as part of the broadcast signal. This broadcast message includes the time difference in whole seconds between GPS time and UTC. During 1996 GPS time minus UTC time was 11 seconds. Also included in this message is the rate and time difference estimate between GPS time and UTC(USNO MC) modulo one second. This allows a receiver, in principle, to calculate an accurate estimate of UTC(USNO MC). The mission goal is 28 ns (1 sigma). Outside of the purposeful current degradation of the GPS signal (called Selective Availability, SA) by the DoD for security purposes, this calculation may have an accuracy of about 10 nanoseconds (ns) on an rms basis. Since USNO has been successful in predicting UTC to within about 10 ns, combining these two independent error sources yields a real-time potential uncertainty for UTC available from GPS at about the 14-ns level. In practice, SA prohibits achieving this accuracy level unless special clock systems and filtering techniques are employed. The SA degradation can be filtered away.
