I have fooled a bit with using a moisture meter under varying conditions.
By the way, there is a ton of good info here that makes my heart smile. I start another 12 days in a row in less than 12 hours, who knows when I will stop by again.
For woodburners like us, the cheapie 2 pin type meters are more than adequate. If you have some mahogany boards seasoning in your garage for 9 years and you are wanting to build a freestanding pendulum clock for a grandchild, look at the $400 meters. Compared to seasoning lumber, seasoning firewood is a cakewalk, the $30-$50 2 pin meters are more than adequate for firewood.
Most of these are going to be calibrated to Douglas Fir at +70dF. If you got any tree that grows in North America under the pins, at +70dF, the reading on the meter is going to be within 1-2%. So any tree grown in North America, tested as below, at +70dF, if you see 20% on the meter the actual laboratory grade number will be somewhere in the 18-22% range, you are golden, burn it. Mind you, if the meter says "30%" the correction factor could be more than 2%, but you can't burn that anyway.
One thing I found digging around, for softwoods - spruce pine fir- the correction factor at +55dF is "+1." I happen to keep my garage at +55dF, and I burn softwood only. So when I bring wood from the back lawn into the garage and bring it up to +55dF over a couple days, and my meter reads 19%, the laboratory MC is probably closer to 20%, but I can burn it.
Be advised that moisture meters cannot detect ice. I tried this a few different ways. When I have a split at "15%" per meter at +55dF, aka 16% laboratory, and I take it outdoors and let it cool off to -20dF, the meter will show me "0%." Your samples need to be indoors long enough to thaw out. Ice is not moisture.
For repeatable results, split open a split and stick the pins in, parallel to the grain, on the freshly exposed face. I generally find low numbers on the ends and near the narrow tip of the triangle. The number I want to know is near the middle of the length, and at the thickest part. On a clear piece with no knots this will be near the bark at the middle of the length.
As has already been beaten to death in this thread, if you are burning 25# of wood in four hours to keep your house warm, burning the same 25# of wood in 12 hours will keep your (more efficient) stove running but won't keep your house as warm.