We've been using data loggers from Onset Computer Corporation, especially
the Hobo series of RH and temperature sensors.  They seem to work well,
can be reconfigured as necessary, and are small enough to hide in dioramas
or on top of temporary walls.  Each logger is an inch or so on a side and
perhaps 5/8" thick.  The readings are stored onboard, then downloaded to
computer as desired.  Each logger can be set to record readings at
intervals from seconds to months, with the number of readings limited only
by onboard memory.  The loggers vary from about $100 to $270, depending on
what you want to measure.
 
One nice feature is the ability to reconfigure it as needed, so that if
the unit reaches its memory limit it can either shut down or continue to
record new measurements, overwriting the older ones.  The units run off an
onboard lithium power cell, which is replaceable.
 
Onset can be reached at 508-563-9000, and is located in Pocasset, Mass.
 
 
Alex Barker, Chief Curator
Dallas Museum of Natural History
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