[CAUT] Dampp-Chaser hygrometer specs

[Roger Wheelock]

Hello list,

I have received a few inquiries regarding the accuracy of Dampp-Chaser 
hygrometers.  Customers have purchased the units in quantity, set them 
all up to run side by side, and then have become concerned about the 
results.  We contacted the manufacturer in Sweden and they verified the 
following information.

Measuring range:  20-95%RH
Accuracy within 50-70%RH: +/- 3%RH
Accuracy outside 50-70%RH: +/- 5%RH

I find that these specs are typical for hygrometers priced similarly to 
ours.  Unfortunately, 42% RH could be read anywhere from 37%RH to 47%RH 
when read with these instruments.  We believe, however, that the 
instruments do measure changes in relative humidity quite accurately.  
We had hoped technicians would use them to show piano owners the 
variations in the piano's environment (maximum versus minimum readings) 
rather than use them as scientific instruments.  I use either data 
loggers or high end ($1500 plus) hygrometers in my research.  The old 
saying, you get what you pay for, is really true for hygrometers.

Another thing I occasionally do is find myself questioning the reading 
only to realize a little later that it was set on either the max. or 
min.  I feel pretty dumb when I figure this out, but thought I would 
pass it along just in case.

Thanks,

Roger