This may seem like a flame, and it is not meant to be so.  However, if you
have had your recording hygrothermograph recalibrated (and which springs
replaced...?) after 4 years of use, you have 3+ years worth of less than
accurate records.

Recording hygrothermographs use a hair bundle (or sets of hair bundles) to
respond to changes in %RH (temperature is recorded from bi-metalic strips
and they tend to be very accurate) and major changes in relative humidity
(winter=cold & dry; summer=warm & wet, etc.) in combination with acids and
bases absorbed from the atmosphere (creating deliquescent salts) throw the
hair bundles out of calibration.

Hygrothermographs should be recalibrated after any significant change in
the weather, otherwise their readings may not be dependable.

It is largely for that reason that I began using data loggers nearly 10
years ago; they are less likely to go out of calibration as the weather
changes, and if the readings begin to drift, it is relatively easy to plug
new numbers into the software to compensate for change.

Jack C. Thompson
Thompson Conservation Lab
Portland, OR

http://www.teleport.com/~tcl/index.html


On Fri, 24 May 1996, Indianapolis Art Center wrote:

> I use Abbeon Cal papers and pens--have had no trouble.  In fact, they just
> had to replace the springs (after 4 yrs of use) for my 2 and recalibrate
> them, and they only charged me $10 each plus shipping.
>
> I don't have their number handy, but if you have access to an 800 directory
> you can probably find them.
>
> Julia Moore
> Indianapolis Art Center
>