Extech model MO290 measures moisture in wood and building materials. It measures moisture on a scal of 0 - 100%. When uisng the meter to measure moisture of wood or drywall you must first a referemce reading on a known dry area of the material being measured. That reading will now be your dry reference point (your new zero point). You then base all other reading accordingly from that reading up to 100%
Let us know if you have any other questions. Thanks
Brian McAuley - Extech Tech Support
Thank you for your most recent inquiry.
Model MO290 has a +/-2.5%RH accuracy and +/-3.6F accuracy for the range being displayed in the pictures. The temp readings seem to be within spec. The RH readings on the meter on the left seem to a bit high. The GGP electronically calculated form the RH & Temp readings.
To insure accuracy on all three units I recommend sending the units to Extech to be evaluated and repaired (if needed). This will allow us to verify the accuracies of all the functions for all three meters. We can also calibrate them to insure that they are all reading within the stated tolerances. This will way you know that all three meters will be working correctly.
If you would like to send your meters in to be checked please contact our repair/return department for a return authorization number and other return info. They can be reached at (877) 239-8324 X4 or by email at
http://www.extech.com/instruments/rmarequest.asp . Please contact me if you have any further questions. Thanks.