<html> <body> At 06:04 AM 4/27/07, Terry wrote: <blockquote type=cite class=cite cite=""> You can have a hygrometer calibrated: <a href="http://www.troemner.com/cal_humidity.htm"> http://www.troemner.com/cal_humidity.htm</a></blockquote> I'll have to call them about the costs, I suppose.  It may not be practical to pay $100 to calibrate a $100 psychrometer.   <blockquote type=cite class=cite cite=""> Or you can by one that has been tested to meet certain standards.</blockquote> These (supposedly) have been tested at the factory and are used by field techs in other professions all the time. Mine (the Cooper) reads the same as other psychrometers I've used. The USB-502 (a hygrometer rather than a psychrometer) reads much like the little units from DC.   <blockquote type=cite class=cite cite=""> Also, look at the specs for your hygrometer, most have a limited range of relative humidity for their stated accuracy - accuracy falls off at very high or low levels.</blockquote> I looked at them closely before I bought it.  They're on the WWW site posted in the message and on the TDS that came with it. When it's real dry the RH readings from the Cooper are much lower than those from more "standard" gauges. While the church I mentioned read 3.8% the DC unit read 16%. On the other hand, now that humidity levels are rising they are fairly close to the same readings. <x-tab>        </x-tab><x-tab>         </x-tab>John <x-sigsep></x-sigsep> <div align="center">------------------------------- John Musselwhite, RPT  -  Registered Piano Technician Musselwhite Piano Services - Calgary, Alberta Canada Office/cel (403) 246-7717 Fax (403) 255-5268 Outside of Calgary call Toll Free:  1-866-95-PIANO (1-866-957-4266) "Three Generations of Experience" </div> </body> </html>