Systematic asymmetry. 1. A condition of the bits not being written straight across a magnetic tape. It occurs when a magnetic tape is not mounted properly with respect to the magnetic heads. The tracks may deviate from their proper position and produce crossfeed, time displacement between channels, parity errors, etc. 2. In magnetotellurics, an invariant of the tensor impedance which indicates the amount of three-dimensionality. It is zero for one- and two-dimensional models with noise-free data. 3. See skewness. 4. To distort.