Quote:The textbooks don't show this to be true. I don't know how to post pictures here yet, but if you Google 'Psychrometric Chart' you will see the correlation between moisture and relative humidity. It is not linear as you suggest. And luckily indoor concrete slabs are relatively stable in temperature, and we are to test at service temperature.
But people do go away from home and sections of commercial buildings HVAC get shut down, even overnight when these buildings are inhabited. So tetsting at service temp is simply a snapshot in time and does not mean that will be the same forever.
I have to say if I am going to test ASTM-2170 method I believe the RapidRh is the best because your testing only down at the bottom of the hole as instructed,. The other probes that hang in the holes even though the air pocket is equilibriated must have a diffency factor because the top part of the concrete is dryer so not a true reading at 40%. Yes, I have watched the infomercial.