MIL-HDBK-1908 Definitions of Human Factors TermsThis handbook defines terms frequently used in human factors standardization documents by providing common meanings of such terms to ensure that they will be interpreted consistently and in the manner intended.

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MIL-HDBK-1908B

Alphanumeric gen/uci. A descriptive term used to define a character set containing the letters of an ethnic alphabet, the digits 0 (ZERO) through 9, and generally special symbols and punctuation marks.

Angle of incidence gen. The angle between the line of direction of anything (as a ray of light or line of sight) striking a surface and a line perpendicular to that surface drawn to the point of contact. See Figure 2.

FIGURE 2. Angle of Incidence

Anthropometric dimensions gen. Measured dimensions that describe the size and shape of the human body. These dimensions are often presented in the form of summary statistics that

describe the range of body dimensions that are observed in a population. Anthropometric terms are defined by MIL-HDBK-743.

Anthropometry gen. The scientific measurement and collection of data about human physical characteristics and the application (engineering anthropometry) of these data to the design and evaluation of systems, equipment, and facilities.

Articulation index (AI) snv. A predictive estimate of speech intelligibility. The AI is a weighted number between 0 and 1 that maps onto speech intelligibility in a non-linear function from

0% to 100%. It can be used to predict intelligibility using different vocabulary sizes and complexities. The AI is computed from a weighted sum of speech-to-noise ratios in several frequency bands. There are three generally accepted AI methods: 20-band method, the third octave-band method, and the octave-band method. The 20 -band method is considered the most accurate and the octave-band method being the least accurate. See ANSI S3.5. (Also see "Speech intelligibility.")

Assembly acq. A number of parts or subassemblies or any combination thereof joined together to perform a specific function and capable of disassembly. (Examples, Power-shovel front fan assembly, audio frequency amplifier.) Note: The distinction between an assembly and a subassembly is determined by the individual application. An assembly in one instance may be a subassembly in another where it forms a portion of an assembly.