I have a Protimeter meter made by GE.The readings are not like a Tramex reads.Like the concrete I tested the other day was in the 18 to 20 range.I believe it reads in wood% terms.It does have sound and color alerts as well.Is anyone familiar with this meter?Is a conversion chart available?It is invasive and non- invasive.

You can't test concrete with a wood moisture meter .

Which model do you have? Actually, many wood meters can be used for testing concrete, although sometimes you may have to drive nails into the concrete to use as contact points for the pins. Some Protimeter models measure wood and concrete, as well as drywall and other building materials. Go to http://www.gesensing.com/protimeterproducts/ and you can view the manuals, etc. for each model.

A meter is useless if you don't know what the readings mean.

My Delmhorst meter will check concrete if I use nails, but no manufacturer will accept this type of testing method. I now use a Tramex Concrete Encounter and even then, some manufacturers want a CC test or RH probes. My personal opinion is taping down 3x3 plastic and checking it after 48 hours is just as good a way as any.