Typical calibration setup for cm VLBI (left) and international LOFAR (right). Note that in some cases the target may itself function as the secondary calibrator. A secondary calibrator is not always required for cm VLBI, but will almost always be needed for international LOFAR, unless the primary calibrator is fortuitously close. The larger field of view of LOFAR means that both the primary and secondary calibrators will always be observed contemporaneously, unlike in cm VLBI, where nodding between the primary calibrator and target is typically required (shown by the double arrow in the left panel).