In response to your query about hygrothermographs:

(1) A data logger does not accurately calibrate this instrument.  Both data
loggers and hygrothermographs should be calibrated with a psychrometer,
either swing or electric.  Psychrometers are the only equipment that provide
accurate RH levels.

(2)  Where are your hygrothermographs from?  The brand name and supplier
location should be listed on the machine.  Companies that sell this
equipment have extra hair and pens.  Here are the most common suppliers:
Cole-Parmer Instrument Company, 800-323-4340
Conservation Materials (sell an English recording hygrothermograph),
702-331-0582
NovaLynx, 916-477-5226

(3) A little more life can be given to a recording hygrothermograph by doing
the following:
      a. brush dust off the hairs with a fine sable brush
      b. take the machine into a very humid area (such as the bathroom while
you are showering) for an hour or two, and then back into the regular museum
environment. This regenerates the flexibility of the hair for a time.

(4) If you calibrate the machine with a psychrometer, it should work well
for awhile.  Note the rate of drift (ie. does it need re-calibration in a
month, a week, or a year?)  Usually I check machines every month and only
have to re-calibrate every 6-12 months.  If I have to re-calibrate less than
every 4 weeks, then the machine should be returned to the manufacturer for work.

Good luck!

Helen Alten
Field Services Director
The Upper Midwest Conservation Association
2400 3rd Ave. S.
Minneapolis, MN 55404
______________________________________________
I have six 10 year old recording hygrothermographs - the kind with hair
bundles and a wind-up clock mechanism - forgot to bring the brandname
home.  Although I've recalibrated them using a datalogger running in
"real-time,"  I'm looking for a company that will do it properly,
replacing the hair bundles if necessary.  My predecessor sent one or two
to California at great cost; I'm hoping for someplace on the east coast of
USA.  The guilt of not using them is getting overwhelming, but in their
present state it would be a waste of time.
Thanks.
Will Garrison
Collections Manager
Historic Deerfield, Inc.
Massachusetts