Where does skew collide?

In statistics, skew (skewness) measures the degree to which a distribution leans to one side of its centre, so that one tail is drawn out longer than the other; a symmetric distribution has zero skew. Karl Pearson introduced the term and its moment-based coefficient in his 1895 study of skew variation in homogeneous material, treating asymmetry as a property to be measured rather than assumed away. Here skew is a number describing the shape of a distribution, not a timing offset between signals or an angle between a bridge and its supports.[1]

Unit

One standardized third moment (the coefficient of skewness), dimensionless.

Recovery means

Compare the lengths of the two tails about the mean, or compute the standardized third central moment.

Measured by

Estimated from sample moments of observed data.

In synchronous digital design, clock skew is the spatial variation in the arrival time of the same clock edge at different registers, caused by unequal path delays through the clock distribution network. Eli Friedman's 2001 review in the Proceedings of the IEEE treats skew as a first-class timing quantity that can both limit and, if scheduled deliberately, improve a circuit's maximum clock rate. Here skew is a time difference between signal arrivals, not the asymmetry of a distribution.[2]

Unit

One time difference between clock arrivals, in seconds (typically picoseconds).

Recovery means

Measure the arrival time of one clock edge at two sequential elements and take the difference.

Measured by

Extracted from timing analysis of the clock tree or on-chip measurement.

In bridge engineering, skew is the angle by which the line of support (abutments or piers) departs from a right angle to the direction of traffic, producing a parallelogram rather than a rectangular deck. Menassa and colleagues (2007) show in the Journal of Bridge Engineering that increasing skew angle redistributes moments and shears in reinforced-concrete slab bridges, so skew is a design parameter with structural consequences. Here skew is a physical angle in a structure, not a statistical moment or a clock-timing offset.[3]

Unit

One angle between support line and the normal to the span, in degrees.

Recovery means

Measure the angle between the abutment line and a line perpendicular to the roadway.

Measured by

Read from bridge geometry or design drawings.