I guess we'll have to look into this at the ATM meeting with Dr Oliver.
Tandy W. Carter Jr.
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----- Original Message -----
From: "Howard L. Cohen" <[log in to unmask]>
To: "Tandy W. Carter Jr." <[log in to unmask]>;
<[log in to unmask]>
Sent: Wednesday, January 24, 2007 11:48 AM
Subject: PC Timing for Occultations
> The problem with PC clocks is not entirely due to errors in the displayed
> time but the internal software clock, which is typically a poor
> timekeepers since timing uncertainty is limited by the stability of
> interrupt requests. Changes in interrupt request rates cause the clock to
> gain or lose time. Also, if you leave your computer turned on for awhile,
> the software clock might be off by possibly a minute or more. Poorly
> behaved software may also use the timer-counter for other purposes and
> change the interrupt rate making the clock keep poor time.
> The display can also cause problems. You can get software that will
> display the time to the nearest second not just to the minute. So this is
> not a problem. However, the software clock also has limited resolution in
> that it can only display values that are even multiples of time interval
> between interrupts. So, a time as 00:00:01.00 might be displayed as
> 00:00:00.98 and 00:00:01.04. Of course, this may be accurate enough for
> your purposes so the problem, again, is not with the display but with the
> internal software clock.
> Thus, even if you synchronize right before observing, the software running
> on your PC during your observing session might screw up the time unless
> you constantly synchronize the clock.
> Note that this problem seems to be the reverse of many GPS units which may
> have good internal times but inaccurate displayed times.
> John Oliver mentioned that cell phones can produce accurate times. I know
> little about this but some research suggested that some but not all cell
> phones might give good times. However, there is another problem. Many
> cell phones (like mine) only display the time to the nearest minute, which
> makes them less useful as accurate time pieces.
> At 10:34 AM 1/24/2007, Tandy W. Carter Jr. wrote:
>> I know the clock in my laptop doesn't keep good time. So, what I do is
>> I synchronize the clock right before I go out to do my astronomy at home,
>> or I synchronize it right before I load it up into the car to go to the
>> star party. I also run only the programs absolutely necessary for my
>> planned astronomy for the evening. Of course, I wonder if it is the
>> displayed time that is bad and not the internal time. I would think that
>> a timing chip running at the speed of modern computers would keep the
>> time spot on. However, you're probably right that the displayed time is
>> not accurate at all. Since the time on my laptop is only displayed to the
>> minute. I don't know how SoftwareBisque handles the time it gets for the
>> FITS header CCDSoft uses.
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