An optical disc storing a copyrighted digital product has a data area in which N processed parts are provided in order to certify that the stored digital product is an original one. A low pressure EGR system is also disclosed. Said locking device comprises one or several tongues being swingable between two positions, a first position in which the tips of the tongues can engage said male elongate connector part and a second position in which the tips of the tongues will not engage the male elongate connector part. Using sum frequency generation, light for sodium excitation, such as for a guide star, can be generated with the optimal modulation of spectral and temporal properties. The gain blocks may be partitioned into steps that represent particular gain values within a range associated with the gain block.