I have never found any that were all that accurate. I just test a sample piece of wood by zeroing it out to see what the moisture content is and assume the rest is about the same since it is all kept in the same enviorment. 80 to 85 degrees and 40% to 45% humidity. I have a small room I built to store wood.
I use one of the cheaper Lignum moisture meters. They cost under $100 and can be found at Woodcraft. Make sure it will measure down to 6%. I have had it for years and it still works fine.
Chris www.cuesmith.com www.internationalcuemakers.com