General Tools and Instruments MMH800 - Manual (Page 9)

Some measurement tips:
1. To locate the source of a leak behind wood, plaster, drywall or a
ceiling, make measurements at different locations. The leak is
where the meter displays the highest reading.
2. Never use force to drive the test pins into a hard surface.
3. When measuring the moisture level of soil, surface readings will be
lower than readings with the test pins deep in the soil.
ACCOUNTING FOR TEMPERATURE AND HUMIDITY
Measurements of wood moisture level are skewed by two variables: ambient
humidity and the density of the wood species. The best way to compensate for
the effect of these variables is to develop your own moisture level curves,
based on your experience working with different species of wood on a day-to-
day basis in your neighborhood.
For example, the humidity level affects the dryness of interior wood considered
“acceptable” for finishing. In the steamy Deep South, where 60% relative
humidity is the norm, fine carpenters have learned how to work with wood with
11% moisture content. But in bone-dry Nevada, Utah, and Arizona, where 30%
humidity is common, the same piece of wood would have to have less than 6%
moisture to be considered ready for finishing.
Moisture levels are just as important to know when joining wood, but for a
different reason. If two work pieces have different moisture levels when they
are joined, when they dry out they will contract by different amounts at
different rates. In the extreme, the result could be a warped board or a
weakened joint.
Temperature also affects moisture levels to the extent that it affects relative
humidity levels. The hotter the air, the more water it can hold. A relative
humidity level of 50% means that the ambient air is holding only half the
moisture is it capable of holding.
The MMH800’s split-screen lower display can help you develop your own
custom moisture level curves by providing real-time temperature and humidity
readings. Both measurements are made and displayed continuously whenever
the meter is powered on.
The meter’s default temperature unit is degrees Celsius (°C). To change the
measurement unit to degrees Fahrenheit (°F), press the button. Each
time the meter is powered on, the unit reverts to the default °C. If you prefer to
work in °F, you must press the button to begin each measurement
session.
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