Semi-major axis of the photocentre as measured with Gaia using the GASTON method (blue squares). The circles represent the semi-major axis derived if an inclination of 90° (edge-on system) is assumed. Green points are HIPPARCOS measurements or upper limits, as explained in Sect. 5. The red squares correspond to a measured Gaia excess noise with a marginal probability smaller than 0.001. The cyan point is the result found in the HIPPARCOS double and multiple systems catalogue. The magenta square is the speckle measurement of Tokovinin (2014) for HD 106888.