From: nospam@de-ster.demon.nl   
      
   Ross Finlayson  wrote:   
      
   > On 11/01/2025 05:43 AM, J. J. Lodder wrote:   
   > > Paul.B.Andersen  wrote:   
   > >   
   > >> Den 31.10.2025 13:21, skrev Maciej Wo?niak:   
   > >>>   
   > >>> GPS clocks are adjusted down by (1 - 4.4647e-10)   
   > >>> so the adjusted clock will measure a mean solar day   
   > >>> to last 86400 s, and the clock will stay in sync with UTC.   
   > >>   
   > >> Right.   
   > >>   
   > >>>   
   > >>> I.e. where The Shit is predicting the measurement   
   > >>> result of 86400s+37(afair)us, the real measurement   
   > >>> result is 86400, with the precision of an acceptable   
   > >>> error. Common sense has been warning your idiot guru.   
   > >>   
   > >> Lets take this one step at the time:   
   > >>   
   > >> 1. A clock on the ground which is running according to   
   > >>      the SI definition will measure a mean solar day to   
   > >>      last 86400 s.   
   > >>   
   > >> 2. SR predicts that a clock in GPS orbit which is running   
   > >>      according to the SI definition will measure a mean solar   
   > >>      day to last 86400?(1 + 4.4647e-10) s ≈ 86400s + 38.6 ?s   
   > >>   
   > >> 3. When a clock in GPS orbit is adjusted to run slow   
   > >>      by the factor (1 - 4.4647e-10) compared to the SI-definition,   
   > >>      then the clock will measure a mean solar day to last 86400 s.   
   > >>   
   > >> Please explain why the real measurement in 3.   
   > >> do not confirm SR's prediction in 2.   
   > >   
   > > You shouldn't allow yourself to be dragged   
   > > into this 'mean solar day' nonsense.   
   > > There is no way that a 'mean solar day' can be measured   
   > > to anything like the accuracy of an atomic clock.   
   > > That is precisely the reason why the astronomical definition of the   
   > > second was given up, long ago.   
   > >   
   > > So the 'mean solar day' is by definition nothing but   
   > > 86400 SI seconds. (of proper time)   
   > > And of course 86401 seconds, once in every three years or so.   
   > > The 'mean' can be left off.   
   > >   
   > > What is really mesured these days   
   > > is the actual orientation in space of the Earth.   
   > > We have the IERS to keep track of that,   
   > > nearly instantaneously, to centimeter accuracy.   
   > >   
   > > Jan   
   > >   
   > >   
   > >   
   > >   
   > >   
   >   
   > No, it's always 86400 seconds.  (By definition, ....)   
   >   
   > The midnight problem then and skew make it so   
   > that the SI units themselves are merely heuristic,   
   > or nominally non-heuristic.   
      
      
   From Wikipedia:   
   ===   
   In specific applications, the definition of a day is slightly modified,   
   such as in the SI day (exactly 86,400 seconds) used for computers and   
   standards keeping, local mean time accounting of the Earth's natural   
   fluctuation of a solar day, and stellar day and sidereal day (using the   
   celestial sphere) used for astronomy. In some countries outside of the   
   tropics, daylight saving time is practiced, and each year there will be   
   one 23-hour civil day and one 25-hour civil day. Due to slight   
   variations in the rotation of the Earth, there are rare times when a   
   leap second will get inserted at the end of a UTC day, and so while   
   almost all days have a duration of 86,400 seconds, there are these   
   exceptional cases of a day with 86,401 seconds (in the half-century   
   spanning 1972 through 2022, there have been a total of 27 leap seconds   
   that have been inserted, so roughly once every other year). It is a   
   non-SI unit that is accepted for use with SI.   
   ====   
      
   Nothing wrong there,   
      
   Jan   
      
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