Despite the effort to minimize thermo-elastic deformations and the effort to make the platform as stiff and stable as possible, small residual variations exists. A secondary objective for the inter-calibration is therefore to assess the size of these residual errors, e.g. gravity release effects.
Finally, the mounting of the sensor units to the stiff optical bench will cause stresses to be built into the mounting interfaces. These stresses may cause minute changes to the internal calibration of the sensors. A third objective of the inter-calibration is therefore to verify the pre mounting calibration of the sensor units.