How will the deviations in flatness be recorded?
In most cases, a straightness reference device (e.g. polished Zerodur rule) is placed on the carriage of the positioning system. The surface of the straightness reference device is scanned with a vertical measurement probe while the system is moving. With particularly long travels, the straightness reference device is placed beside the positioning system and the vertical measurement probe is driven by the carriage of the positioning system.
The rise of the profile logged is compensated using a compensation line. The deviation in flatness is half of the peak value of the measured, compensated profile. The real profile can deviate from the ideal both in both negative and positive directions. Installation location and load changes can have an influence on the amount of deviation in flatness.