| 摘要 |
An apparatus is provided for generating a pulse train, the apparatus comprising a member having a plurality of spaced marks disposed thereon with at least one of the spaced marks being a reference mark. The member is in communication with means for generating the pulse train as the plurality of spaced marks move. Additionally, the pulse train has a periodicity defined by the same edge of two successive pulses and the plurality of spaced marks are configured so that the periodicity of the pulse train remains constant.
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