INTRODUCTION
Thank you for purchasing General Tools & Instruments’ MMH800 4-in-1 Pin/Pad
RH Moisture Meter. Please read this user’s manual carefully and thoroughly
before using the meter.
The MMH800 is designed for use in woodworking, water damage restoration,
building construction and home renovation. Examples include:
• Checking for moisture on or below the surface of carpets
• Measuring the surface moisture and/or moisture content of wood,
drywall or concrete before painting, wallpapering, sealing or treating
• Locating water leaks in roofs, floors and walls
• Selecting dry lumber
Because it can measure ambient temperature and humidity in addition to
moisture level, the MMH800 is particularly suitable for water damage
restoration projects.
The meter has two LCDs: one displays moisture level and the other—a split-
screen display—monitors temperature and humidity. A dedicated front-panel
button selects the default temperature unit (degrees Fahrenheit or degrees
Celsius).
The 4-in-1 part of the meter’s name refers to its ability to measure:
1) temperature; 2) relative humidity; 3) moisture level using a pin sensor; and
4) moisture level using a pad sensor. The meter has both kinds of sensors, with
a pair of pins on top and a split metal pad on the back. Both sensors base their
measurements on the relationship between the moisture content of a material
and its electrical conductivity. The wetter a material, the higher its conductivity.
In both cases, the sensors serve as the electrodes of a conductivity meter
optimized for measuring moisture content.
Which sensor should you use?
It depends on the application. The pad sensor is the only choice for measuring
surface moisture of materials like finished wood, paint or wallpaper that cannot
be marred by pinholes. If measurement accuracy is important, the pin sensor is
the better option because pins can detect moisture below the surface that the
pad sensor cannot.
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