Several types of moisture meters are currently used to nondestructively estimate the moisture content of wood. Because these instruments do not directly measure the amount of moisture in wood, the reading is rarely equal to the "true" moisture content that would be determined by an accepted primary standard (i.e., by ovendrying or distillation). Moisture contents determined using these nondestructive, or nonintrusive, instruments are inferred from actual measurements of selected physical properties of wood (e.g., a conductancetype meter measures the resistance to ˇ®the flow of direct current which varies as a function of the amount of water in wood). These instruments can be used for sorting green lumber, for monitoring the moisture content of lumber in a kiln for process control and/or end-point determination, and for quality control purposes in post-drying applications. Postdrying applications can include a range of situations, including uses immediately after drying (e.g., using an in-line meter for lumber on the dry chain) and "in-service" applications (e.g., using a hand-held meter on a joist in the crawispace of a house). With each of these applications, the location and distribution of moisture in the wood, plus other wood properties, such as relative density, can affect the meter reading. In order to obtain reliable readings from moisture meters, it is essential to understand the factors that influence their operational characteristics. This paper reviews existing techniques that are used to estimate the moisture content of wood and discusses the potential limitations of instruments based on these techniques. Online

• measurement: moisture content

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