| 摘要 |
An alignment apparatus includes first and second alignment devices (1) and means (9) for mounting each of the first and second alignment devices in spaced relationship one behind the other and such that one alignment device is at a higher level than the other alignment device. Each alignment device (1) includes a plate member having a surface comprising at least one area of reflective material and at least one area (3, 5) of non-reflective material. The areas of reflective material and of non-reflective material are configured such that, when an elongate beam of electromagnetic radiation is incident on both of the first and second alignment devices, the pattern of reflected radiation varies according to whether both of the first and second alignment devices are aligned with the beam.
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