In the area of mounting and spot-welding of body-in-white, absolutely accurate robots are installed as measuring instruments, replacing expensive coordinate and other external measuring machines. Measurement technologies based on industrial robots play an increasingly important role. Such applications require highly accurate robots. Prior to deployment of highly accurate robot, however, it needs to be ensured that the implemented robot model fits the real model. Robot calibration can offer a significant opportunity to improve the positioning accuracy and to cut production costs. Existing calibration approaches fail to capture geometric and elastic effects occurring in the robot forward kinematics. Therefore, in this work an extended forward kinematic model incorporating both geometric and elastic effects has been developed in which the positioning accuracy of a manipulator, with or without an accurate internal robot model in the robot controller, is improved.