This paper reports on the calibration routine developed for an absolute measurement of the mean radius and the ovality
of a ring. By means of six laser triangulation sensors, the measurements are performed in-process in a furnace during
heat treatment. The lack of precise information about the exact position and direction of the sensors and the minimal
accessibility of the ring in the furnace is challenging and leads to a complex calibration routine. The calibration includes
the application of gauge rings with different diameters. The developed routine is described and calibrated measurement
results are compared with coordinate measurement machine (cmm) data. Concerning the ring radius (~ 72.5 mm), the
comparison exhibits a deviation to the cmm data of less than 35 μm.