In a sequential circuit, the arrival of a signal at two or more places at significantly different times, when it should have arrived at more nearly the same time. Skew is said to be present when the difference in arrival times is great enough to cause or threaten malfunction of the circuit; this difference (usually measured in nanoseconds) is called the amount of skew. Most commonly, concern is expressed about clock skew, which is the skew in clock signals (for which the phenomenon has usually the most serious consequences). Skew may be caused by component malfunction, or bad physical construction, but most often by bad logic design of the circuit. See also race condition.