[LEAPSECS] drawing the battle lines

[Joseph Gwinn]

On Wed, 20 Mar 2013 20:16:49 -0700, Rob Seaman wrote:

> On Mar 20, 2013, at 6:02 PM, Joseph M Gwinn <gwinn at raytheon.com> wrote:

>> I would propose that ITU is using continuity and uniformity in their 

>> mathematical definitions, implying that the intent is that at least 

>> in definitional theory, UTC be mathematically continuous with all 

>> its derivatives (noise being ignored).  This would exclude step 

>> discontinuities (leap seconds) and piecewise linearity (like UT1).  

>> Given that the length of a SI second is constant, what's left is a 

>> UTC that is a constant offset from TAI, where the offset changes 

>> only if so ordered.

> 

> Relative to what?  If UT1 is an angle, then derivatives with respect 

> to "angular time" are stationary, and derivatives with respect to 

> atomic time vary.  At any rate, continuous is still the wrong word.  

> All the derivatives of sin(t) are continuous, but the function itself 

> is non-monotonic.


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.  No trig functions need apply.

It's pretty clear that ITU intends to make UTC essentially like TAI, 
but not just as a paper clock.

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.

Joe