Similar to Fig. 3, but illustrating the dual-field off-axis observing strategy. In this case, a roof-mirror is used to separate the field, and two sequences are required. In the science sequence, the FT fibre is positioned on an appropriately selected FT target, whereas the SC fibre is centred on the science target. In the calibration sequence, a binary star is observed multiple times while swapping the position of the two fibres. If the science target is appropriate for fringe-tracking, the calibration can be performed on the science target itself. If this is not the case, the calibration sequence must be performed on a separate binary calibrator.