you can check the accuracy of digital meters by testing them on your skin. from memory it should read about 8%, but im not sure anymore.
but then even with a meter, you can only see the real moisture value when you cut open the piece of wood and measure at the center. measuring on the end of boards or the outside edge will give a lower value than is real.
i bought one to check the humidity of wood at the lumberyard before buying, but it's pointless unless they let you cut their wood in half to check.