On Tue, 22 Feb 2011, Bo Berglund wrote:
On Mon, 21 Feb 2011 07:23:54 +0100, Bo Berglund
<[email protected]> wrote:
When I run a test against a fairly accurate GPS time source I see that
there is an uncertainty of about 16 ms in the time given such that if
GetTickCount is executed at exactly 1 second intervals the last two
digits of the value is not the same as it should be.
Instead it slowly (over a period of 16 seconds) reduces by 16 ms and
then suddenly restores to a max value.
It is like a superimposed sawtooth with an amplitude of 16 ms.
The posted variation is apparently a Linux platform compatible version
that returns a millisecond value the same way as the Windows version
does, since there is no Windows GetTickCount API call in Linux.
I used this also on Windows in my tests and then the value does not
exhibit the sawtooth anymore. So I assume that Now() gets its time
from another source than the timer counter driving GetTickCount and
this is more accurate.
I should have added that instead of a sawtooth like noise component
using Frac(Now()) * 24*3600 to get the second since midnight gives
random noise in the seconds values of about 3-4 ms.
Another observation is that there seems to be no data smaller than ms.
If I format this value as a float with more decimals than 3 I always
only see zeroes.
That is logical, since TDateTime only is accurate to millisecond precision.
Michael.
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