Industrial Augmented Reality (AR) applications require fast, robust, and precise tracking. In environments where conventional high-end tracking systems cannot be applied for certain reasons, marker-based tracking can be used with success as a substitute if care is taken about (1) calibration and (2) run-time tracking fidelity. In out-of-the-laboratory environments multi-marker tracking is needed because the pose estimated from a single marker is not stable enough. The overall pose estimation can be dramatically improved by fusing information from several markers fixed relative to each other compared to a single marker only. To achieve results applicable in an industrial context relative marker poses need to be properly calibrated. We propose a semi-automatic image-based calibration method requiring only minimal interaction within the workflow. Our method can be used off-line, or preferably incrementally online. When used online, our method shows reasonably good accuracy and convergence with workflow interruption of less than one second per incremental step. Thus, it can be interactively used. We illustrate our method with an industrial application scenario.