[LEAPSECS] drawing the battle lines

[Joseph Gwinn]

On Wed, 20 Mar 2013 22:46:01 -0700, Rob Seaman wrote:

> On Mar 20, 2013, at 8:28 PM, Joseph Gwinn <joegwinn at comcast.net> wrote:

> 

>> True enough, but beside my point.  The relationship between UTC and UT1 

>> is piecewise linear between leap seconds, so there are steps in the 

>> first derivative at the joints between lines,and steps in zeroth and 

>> first derivatives at the leap seconds.

> 

> Ignoring the perpetual refrain about leap seconds being merely a 

> representational issue, Kevin's question was about point 9 of the 

> CCTF recommendation, which is an assertion about UT1 itself.  Saying 

> UT1 is unacceptable as a time scale is like saying John Harrison's 

> descendants should refund the longitude prize.  Many quantities can 

> serve as timelike independent variables.


I'm just summarizing what I think the ITU intended to say.

Arguing that the ITU is wrong in what they said does not change the 
translation.

 

>> It's pretty clear that ITU intends to make UTC essentially like TAI, 

>> but not just as a paper clock.

> 

> If ceasing leap seconds would manage this transmogrification from 

> paper clock to real clock, than simply applying DTAI manages the same 

> thing.


I was just observing what their direction appears to be.  I don't have 
a vote in the ITU.



>> And I will say that in the big radars I build, leap seconds are a real 

>> problem, one that we solve by using GPS System Time in all but human 

>> interfaces.

> 

> So you recognized that UTC did not match your project requirements 

> and used a different widely available time scale that did.  How 

> exactly were you disadvantaged?  


The disadvantage was that many people believe UTC to be suitable, but 
don't notice or deal with the leap seconds, which is devastating in 
radar trackers for instance.  With one dish radar system, we were 
forced to use UTC because a major piece of reused software couldn't 
handle conversion between GPS System time and UTC, and so needed to run 
only UTC.  To verify if this would work, we artificially inserts both 
plus and minus time steps of one second.  Adding a second caused no 
visible disturbance.  Subtracting a second caused some gyrations, but 
these soon dissipated.  The dish rotation period was 12 seconds, so one 
second is almost 10% error in the detection timestamps, and this was 
enough.  A faster rotating radar would not have been able to handle 
such a step discontinuity. 



>   The ITU is attempting to turn one 

> flavor of time scale into another.  The fallacy is the notion that we 

> shouldn't have two time scales in the first place.


Well, standards groups do do these things, and over time it is a great 
help.  I would look to the history of machine screw threads for a 
parallel.  

In my case, ceasing to have leap seconds will be helpful.  In your 
case, it's not helpful.  This is also true of all standards, which are 
thus decided by the balance.

Joe