This recording technique has many potential sources of timing errors. If the mechanism runs at an absolutely constant speed, and never varies from moment to moment, or from the time of recording to the time of playback, then the timing of the playback signal is exactly the same as the input. However, imperfection being inevitable, the timing of the playback always differs to some extent from the original signal. Longitudinal error (error arising from effects in the long direction of the tape) can be caused by variations in the rotational rate of the capstan drive, stretching of the tape medium, and jamming of tape in the machine. Transverse error (error arising from effects in the cross-tape direction) can be caused by variations in the rotational speed of the scanning drum and differences in the angle between the tape and the scanning heads (usually addressed by video tracking controls). Longitudinal errors are similar to the ones that cause wow and flutter in audio recordings. Since these errors are not so subtle and since it is standard video recording practice to record a parallel control track, these errors are detected and servos are adjusted accordingly to dramatically reduce this problem.