• MLCD • microwave liquid crystal display • mm • millimeter • MOOT • method of optimal truncation • MPa • megapascal • mpg • miles per gallon • mrem • millirem • mSv • millisievert • MTF • modulation transfer function • mV • millivolt • MVp • megavolt peak • n • neutrons • N • newton • n • index of refraction; fringe number; number of tests • • average sample size • n • unit vector normal to the surface • N • number of cycles; summation index; fringe order; length of the near field • N K • Knudsen number • N Re • Reynolds number • NBS • National Bureau of Standards • NDE • nondestructive evaluation • NDI • nondestructive inspection • NDT • nondestructive testing • Nd: YAG • neodymium: yttrium-aluminum-garnet (laser) • nm • nanometer • NMR • nuclear magnetic resonance • No. • number • NTSC • National Television Systems Committee • OD • outside diameter • Oe • oersted • OSHA • Occupational Safety and Health Administration • oz • ounce • p • probability • P • pressure • Pa • pascal • PC • printed circuit • PCB • printed circuit board • pH • negative logarithm of hydrogen ion activity • PH • precipitation hardening • PIND • particle impact noise detection • PLC • programmable logic control • P/M • powder metallurgy • PMT • photomultiplier tube • POD • probability of detection • POFA • probability of false alarm • ppm • parts per million • ppt • parts per trillion • psi • pounds per square inch • psig • gage pressure (pressure relative to ambient pressure) in pounds per square inch • Q • calibrated leakage flow • r • number of levels of each factor; original pixel value; radius; range • R • roentgen • R • resistance; reflection coefficient; rise time; gas constant; radius • R a • arithmetic average roughness • R s • effective shunt resistance • rad • radiation absorbed dose • radac • rapid digital automatic computing • rbe • relative biological effectiveness • ref • reference • rem • roentgen equivalent man; remainder • RF • radio frequency • RFEC • remote-field eddy current • RGB • red, green, blue • RHM • roentgen per hour at one meter • RMM • roentgen per minute at one meter • rms • root mean square • ROC • relative operating characteristic • RSSS • radiographic standard shooting sketch • RTR • real-time radiography • s • second • S • siemens • S • sensitivity; speed; spacing • S • signal input • SAE • Society of Automotive Engineers • SAM • scanning acoustic microscopy • SAT • structural assessment testing • SDD • source-detector distance • SDP • standard depth of penetration • SEC • secondary electron-coupled (vidicon) • SEM • scanning electron microscopy • sfm • surface feet per minute • SiIMPATT • silicon impact avalanche transit time • SIT • silicon intensified target • SLAM • scanning laser acoustic microscopy • SLR • single lens reflex • S/N • signal-to-noise (ratio) • SOD • source-object distance • SOF • shape and orientation factor of the flaw • SPC • statistical process control • SPDT • single pole double throw • Sv • sievert • std • standard • t • time; thickness • T • tesla • T • temperature; transmission coefficient • TAB • tape-automated bonding • TE • transverse electric (mode) • TEM • transmission electron microscopy • TEM • transverse electromagnetic (wave) • TM • transverse magnetic (mode) • TIG • tungsten inert gas (welding) • TOF • time of flight • tsi • tons per square inch • U g • geometric unsharpness • UCL • upper control limit • ULCE • unified life cycle engineering • USAF • United States Air Force • UST • underground storage tank • UT • ultrasonic testing • v • degree of freedom; velocity • V • volume; velocity; variance • VHS • very high speed • VHSIC • very high speed integrated circuit • VLSI • very large scale integration • vol • volume • W • watt • WORM • write once read many • • sample mean • YIG • yttrium iron garnet • yr • year • Z • impedance; atomic number; standard normal distribution • ° • angular measure; degree • °C • degree Celsius (centigrade) • °F • degree Fahrenheit • • direction of reaction • ÷ • divided by • = • equals • • approximately equals • • not equal to • • identical with • > • greater than • • much greater than • • greater than or equal to • • infinity • • is proportional to; varies as • • integral of • < • less than • • much less than • • less than or equal to • ± • maximum deviation • - • minus; negative ion charge • × • diameters (magnification); multiplied by • · • multiplied by • / • per • % • percent • + • plus; positive ion charge • • square root of • • approximately; similar to • • partial derivative • • thermal diffusivity; angle of incidence • • angle of refraction • • shear strain • • skin depth • • change in quantity; increment; range; phase shift • • normal strain; emissivity; dielectric coefficient • • viscosity • • angle • • wavelength; mean free path • • linear attenuation coefficient; magnetic permeability; the mean (or average) of a distribution • in. • microinch • m • micron (micrometer) • • Poisson's ratio; frequency • • pi (3.141592) • • density; resistivity • • stress; standard deviation; electrical conductivity • • summation of • • shear stress • • angle of refraction • • circular frequency (angular velocity) • • ohm o Greek Alphabet • A, • alpha • B, • beta • , • gamma • , • delta • E, • epsilon • Z, • zeta • H, • eta • , • theta • I, • iota • K, • kappa • , • lambda • M, • mu • N, • nu • , • xi • O, o • omicron • , • pi • P, • rho • , • sigma • T, • tau • , • upsilon • , • phi • X, • chi • , • psi • , • omega . National Bureau of Standards • NDE • nondestructive evaluation • NDI • nondestructive inspection • NDT • nondestructive testing • Nd: YAG • neodymium: yttrium-aluminum-garnet (laser) •. single lens reflex • S/N • signal-to-noise (ratio) • SOD • source-object distance • SOF • shape and orientation factor of the flaw • SPC • statistical process control • SPDT • single pole. SAT • structural assessment testing • SDD • source-detector distance • SDP • standard depth of penetration • SEC • secondary electron-coupled (vidicon) • SEM • scanning electron microscopy