moisture meters are one of those you get what you paid for things.  The more money they cost the better the quality and accuracy.  I use a cheap one from harbor freight but i use a postal scale to.  The meter is used to give me a ball park for when my twice turned things are close to dry.  Then i use a scale weighing once a day until i get 3 days of not loosing weight.  weight is a much more accurate measure of how dry it is.  Meters can only measure moisture as deep as you can get the pins in.