Brian Garrett wrote:
It surprises me that the Red Cross needs this kind of accuracy to
begin with.
They don't, of course. What they do have is a requirement for
reasonably good relative interval timing and absolute timestamps. As
with any COTS solution, the biggest problems may be with unspecified
features tossed in "for free" by the vendors.
The only reason a blood bank would need reasonably accurate clocks
is that the units collected have to be used within 72 hours
according to regulations, or so I've read.
42 days currently: http://www.sciencenews.org/articles/20080322/fob1.asp
They also need accurate and reasonably precise timestamps to tag their
workflows, i.e., when did this event happen relative to that event for
a particular center? The collection is preceded by an extensive
questionnaire and health check, too. Workflow logistics is everything.
The interval timing requirements are more precise. A donation must
complete in a certain window of time (so many minutes) or the
resulting products aren't usable. Missing the window by seconds might
well cause the blood (or the donor :-) to be rejected.
Surely at least a few minutes leeway is allowed, and NIST-traceable
accuracy is overkill.
Leeway might be technically acceptable, but the protocol is very
specific and the logistics are not to be trifled with.
Accuracy and precision are not the only issues with traceability. We
shouldn't design solutions pretending that they are.
FWIW, blood banks are usually located in buildings with _lots_ of
fluorescent lights. Good luck getting a radio-controlled clock to
work in an environment like that.
Like I said, the clocks remained synced through several visits
suggesting that they received a signal on a regular schedule. They do
turn the lights off at night, I presume. The underlying clocks are
undoubtedly crap, but likely can't drift very far in a day. I do tend
to donate first thing in the morning.
Rob Seaman
NOAO
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