Amplitude of the differential phases in the uv plane: each uv point is colour-coded with the value of Δφ, the difference of the differential phase at 10 μm to those at the edges of the N-band (λ = 8.2 μm & 13.0 μm). Filled dots denote a phase signal with > 3σ significance averaged over the N-band, empty circles a phase signal with < 3σ significance, i.e. a differential phase consistent with 0.