Using three planar mirror laser interferometers, ISARA measures the position of an object on a table according to the Abbe principle: the functional point is in line with the measuring line to avoid errors in parallax. Positioned in one stiff frame with the probe, the three planar mirror laser interferometers have their virtual intersection point coinciding with the measuring point of the probe

The product table - made from Silicon Carbide (SiC) for its stiffness and thermal stability - is placed on a mirror table that can be moved in X and Y directions over a granite plate using porous media air bearings. A monolithic block of Zerodur deposits the reflective coating directly onto three extremely flat surfaces to form the three mirrors; the mirror block assembly is directly connected to the machine and calibrated within it, allowing for both the flatness and the mutual perpendicularity of each mirror.

Furthermore, the metrology frame containing the three laser interferometers and the probe moves in the Z direction using air bearings, over a granite guiding surface. The interferometers always point to the centre point of the probe tip (fulfilling the 3D Abbe principle) while the metrology frame (also made from SiC) is stiff with no internal degree of freedom, avoiding the need for extra bearings.

The base frame consists of two granite guiding units - one for the X-Y system and one for the Z - joined to form a stable base frame. The air bearing-equipped direct drives for all three directions are each mounted separately from the part they drive.