Left: 3-σ sensitivity versus separation for a completeness level of 80%. Right: completeness in the separation range 6−40 mas versus contrast. Simulations are for a single snapshot pointing (dashed lines) and for five pointing separated by one hour (solid lines). Colours are for the four configurations displayed in Fig. 4. The black curves are for the U1-U2-U3-U4 configuration displayed in Fig. 1. The contrast axes can be scaled for any accuracy on the closure phase (here σ = 0.25deg).