Observation of the calibrator star HD 55185 with VEGA with three telescopes (E1E2W2) at medium spectral resolution (Δλ = 30   nm centered at λ = 735   nm). The tracking of the fringes is done in the near-infrared with the instrument CLIMB. Plots represent the OPD residuals measured on VEGA data for the three baselines. The OPD estimates are done each second (50 short exposures of 20 ms). Note that, according to the principle described in Sect. 2, the fringes are not stabilized around null OPDs. For this specific experiment, we did not used the standard configuration as defined in Table 1.