Where does compression collide?

A state of stress that pushes the particles of a body together and tends to shorten it along the line of loading: the compressive stress is the internal force per unit area that resists the push, and the accompanying compressive strain is the fractional shortening it produces. Gere and Goodno's Mechanics of Materials treats it as the sign-reversed counterpart of tension, with a material's compressive strength being the stress at which it crushes or buckles. The referent is a mechanical loading of solid matter, measured in pascals, and it has nothing to do with squeezing a data file, pinching a nerve, or narrowing a pay scale.[1]

Unit

A shortening stress in a loaded solid, in pascals (force per unit area)

Recovery means

Within the elastic range the body springs back when the load is removed; past the elastic limit it crushes, yields, or buckles permanently

Measured by

Determined in a compression test by loading a specimen and recording stress against strain, up to its compressive strength

The encoding of information using fewer bits than its raw representation, achieved by exploiting redundancy and statistical structure in the data. Huffman's 1952 A Method for the Construction of Minimum-Redundancy Codes gave an optimal way to assign shorter codewords to more frequent symbols, while Shannon's entropy sets the hard limit below which no lossless scheme can go. The referent is a coding operation on symbols, lossless when the original is recoverable exactly and lossy when detail is discarded for a smaller size, measured in bits and compression ratio, not a force on matter, a nerve, or a wage.[2][3]

Unit

A reduction in the bits needed to represent data, in bits or compression ratio

Recovery means

Lossless compression restores the original data exactly on decoding; lossy compression discards detail that cannot be recovered

Measured by

Quantified by compression ratio and bits per symbol, and bounded below by the source's Shannon entropy

A mechanical loading of a peripheral nerve by the surrounding tissue that raises pressure on it and impairs its function, the mechanism behind entrapment syndromes such as carpal tunnel. Rempel, Dahlin, and Lundborg's 1999 review described how sustained pressure obstructs blood flow within the nerve, disrupts axonal transport, and provokes oedema, so that conduction slows and symptoms follow the dose and duration of the load. The referent is a pathological squeezing of living nerve tissue, graded by pressure in millimetres of mercury and by nerve conduction studies, unrelated to a stress in a beam, a coded data stream, or a wage distribution.[4]

Unit

Sustained pressure on a nerve trunk, in millimetres of mercury

Recovery means

Function often returns when the pressure is relieved early; prolonged or severe compression leaves lasting axonal damage

Measured by

Assessed by nerve conduction velocity, distal latency, and the tissue pressure applied to the nerve

A narrowing of the wage distribution so that pay differences between skill levels, seniority, or job grades shrink toward one another. Freeman's 1982 study of union wage practices showed how standardised pay policies compress the spread of earnings within establishments, reducing the dispersion around the average. The referent is a statistical flattening of a pay structure, measured by the variance or percentile spread of wages, and it is a fact about a labour market rather than a force on a solid, a coded file, or a pinched nerve.[5]

Unit

A narrowing of the spread of wages across a workforce, by wage variance or percentile ratio

Recovery means

Not applicable

Measured by

Gauged by the variance or standard deviation of log wages and by ratios such as the 90/10 percentile spread