| 摘要 |
An apparatus for testing for straightness and evenness comprises two vertical displacement transducers (30,31) providing electrical signals representing the relative levels of a reference surface (33) and a test surface (2), respectively. These signals are subtracted at (23) and the difference signal, representing the difference in the levels is fed via an evaluation stage (54) to an indicator (26). To enable the evaluation stage to correct the signal to the indicator for the effects of tilting of the surface under test during the measurement, two further pairs of vertical displacement transducers (39, 40 are one pair) are provided which are disposed respectively in the directions of the horizontal x and y co-ordinates. The two signals from each further pair of transducers are subtracted one from the other at (44) and the two resulting difference signals DELTA alpha , DELTA beta are fed to the evaluation stage (54) which is adapted to effect correction of the first- mentioned difference signal. <IMAGE>
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