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From: Emanuel Berg <embe8573@student.uu.se>
Newsgroups: comp.lang.ada
Subject: Re: how to analyze clock drift
Date: Thu, 20 Nov 2014 21:41:41 +0100
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Date: 2014-11-20T21:41:41+01:00
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"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
writes:

> Yes, that is when you already know the expected
> time. I assumed that the reference clock and the
> clock used in wait are different clocks, deviating
> at constant speed.

Yes, I should have told you. The data I posted
yesterday from the Lisp program - the first trace are
the measured tick times in nanoseconds, and the
intended tick is *1 ms*.

The outputs are by doing the suggested:

    offset = time1 - time2 - DESIRED_TICK

(I wonder if I made a mistake here - I assume I should
put DESIRED_TICK in nanos as well? - and I don't
remember doing that.)

Anyway if this method is good, can I make any
conclusions from the data? For example, how big a mean
would be considered a big drift, how big a deviation
an uneven drift, and so on?

Here is the original data again:

For these clock ticks (in nanoseconds):

    85033108461718
    85033109544537
    85033110621490
    85033111714366
    85033112794112
    85033113871903
    85033114934049
    85033116009605
    85033117089909
    85033118169656
    85033119256945
    85033120336411
    ...

The output is:

    readings: 543
    mean: 1076366.000000
    variance: 14127140.000000
    standard deviation: 3758.608785
    min: 1062145
    max: 1096507

    1082818
    1076952
    1092875
    1079745
    1077790
    1062145
    1075555
    1080303
    1079746
    1087288
    1079465
    1072762
    ...

-- 
underground experts united