These are not actually populated by the code yet. I'm trying to get the
v3 schema frozen as soon as possible; actually using the fields can come
later.
Add some explanation of their value in time.md, along with some general
musing on leap seconds, and a correction on the frequency error of my cameras.
This time, I've given up on svg and am using png. The inline svg seems to be
totally stripped out by github's markdown->html conversion, and img links
don't work because .svg files are served with an incorrect Content-Type.
This is more sophisticated than the current implementation. It's an attempt
to address the problems created by the 9 seconds/day of drift I'm seeing for
long-running streams.
