Optical reversal measurement
To ensure optimum straightness measurement accuracy, the straightness measurement should be repeated with the straightness reflector rotated through 180° so that the 'left hand' and 'right hand' sides are reversed.
After the first set of straightness measurements have been made, remove the straightness reflector carefully from its mounting without disturbing the position of the mounting. Invert and replace the reflector with care, again care being taken not to disturb the position of the mounting. (Where the standard optics mounting kit is used, the clamp block can be removed and inverted with the straightness reflector.)
Provided that the mounting for the straightness reflector was not disturbed and the alignment of the laser beam and position of the straightness interferometer have remained unchanged, the system will be generally aligned except that the tilt adjustment on the straightness reflector will be in the opposite direction to that required. System alignment, including manual removal of slope, should be possible by adjustment of the tilt of the straightness reflector alone.
Now capture a second set of straightness measurements.
The analysed results from the two sets of measurements can be compared; a true measurement (i.e. optimum accuracy) is obtained from the mean of the two.