quarter the wavelength of the laser beam, a light wave reflected by a pit travels half again as long (125% as long to hit the disk and the same to return) as a wave reflects by a land. This way, whenever the laser strikes a pitted groove, the wave and its reflection are dephased by a half wavelength and cancel one another out (destructive interference), so it's as if no light was reflected at all. Moving from a pit to a land causes a drop in the signal, which represents one bit. The length of the groove is what stores the information. The size of a bit on a CD ("S") is standardized and corresponds to the distance travelled by the light beam in 231.4 nanoseconds, or 0.278?m and the standard minimum velocity of 1.2 m/s. In the EFM standard (Eight-to-Fourteen Modulation), used for storing information on a CD, there must always be at least two bits set to 0 between two consecutive 1 bits, and there cannot be more than 10 consecutive zero bits between two 1 bits, in order to avoid errors. This is why the length of a groove (or a land) is greater than or equal to the length needed to store the value OO1 (3S, or 0.833?m) and less than or equal to the length of the value 00000000001 (11S, or 3.054?m).