If you burn with wood you want to make sure the wood is as dry as possible. Burning wet wood (wood with a high moisture content) can consume as much as twice the amount of energy as dry wood for the same amount of BTUs. The reason for this is that, although you may witness a nice flame, a large amount of energy is being used to drive off the moisture as opposed to giving you heat.
An age old way to tell if your wood is dry is to listen to it. If there is a large hiss coming from the log it is boring off moisture. Also you will often see moisture bubbling from the end of the log as the moisture boils off.
Instructions:
With the meter turned on drive the prongs into a piece of wood. Preferably a recently split piece of wood using an inside surface from the split wood. You want to achieve a moisture level of less than 20%.