[time-nuts] humidity and early HP cesium standards

[Steve Allen]

BIPM produces a correction to TAI that is intended to allow the
best reconstruction of what TT would be.  These corrections are
known as TTBIPMyy, where yy is the year that the particular
correction was constructed.

I have plots of several TTBIPM versions, e.g.
https://www.ucolick.org/~sla/leapsecs/ttbipm17.png

The beginning of any TTBIPMyy shows the 1e-10 rate change
that became evident in the early 1970s and was corrected
as of 1977-01-01.

Even after that correction TTBIPM shows an annual wobble.
That annual wobble is more clear in the last plots on
https://www.ucolick.org/~sla/leapsecs/earlyAT.html

Looking back this evokes questions about the HP cesium standards.
I expect that HP had taken pains to be sure that their rate was
relatively insensitive to changes in temperature.
How did HP miss that their rate was sensitive to humidity?

Does anyone have references to literature explaining what was known
about these seasonal rate variations of HP cesium standards?

--
Steve Allen                    <sla at ucolick.org>              WGS-84 (GPS)
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