The term wobble refers to the usually sinusoidal deviation of the pre-groove track on formats such as CD-R, CD-RW, DVD-R, MiniDisc etc. The pre-groove is not a perfect Archimedes Spiral, rather it is 'wobbled' in a sinusoidal fashion. The player detects this wobble from the un-recorded disc and uses it to lock precisely onto the pre-groove track. The amplitude of the wobble is generally very small compared to the track pitch (e.g. about 30 nanometres) and can be a fixed frequency (e.g. for DVD-R) or modulated (e.g. for CD-R).