[LEAPSECS] BBC radio Crowd Science

[John Sauter]

Thank you, Tom and Steve, for your corrections to my misunderstanding. 
Looking at the first part of Steve's table:

> 
> Positive leap second:
> 
> 	TAI           UTC           TAI-UTC
> 	00:00:34.0    23:59:59.0    35
> 	00:00:34.5    23:59:59.5    35
> 	00:00:35.0    23:59:60.0    35
> 	00:00:35.5    23:59:60.5    35
> 	00:00:36.0    00:00:00.0    36
> 	00:00:36.5    00:00:00.5    36

TAI is the fundamental time scale, with UTC derived from it.  As TAI
advances, you can calculate UTC by subtracting TAI-UTC from it.  At TAI
= 34 seconds, TAI-UTC is 35 and the corresponding UTC time is 23:59:59.
 That can be arithmetically correct only if you don't count the leap
second, so let's not count it.

When the TAI time is 35 seconds, you would think the UTC time would be
0 seconds, but because of the leap second it is 23:59:60.  Thus, the
value of TAI-UTC doesn't tell you everything you need to know to
convert from TAI to UTC: you also have to know that there is a leap
second in progress.

When the TAI time is 36 seconds, and TAI-UTC is now 36, the UTC time is
0, which is what you would expect.

I had thought that TAI-UTC was the only information needed to convert
from TAI to UTC, and therefore that it could not be a step function
because of positive leap seconds.  I see now that I was mistaken.  Is
my new belief correct that you need both TAI-UTC and the knowledge that
a leap second is in progress to convert from TAI to UTC?
    John Sauter (John_Sauter at systemeyescomputerstore.com)