I calculated the bouyancy effect of the optical bench, which hangs from three copper berylium blades at the base of the inverted pendulum.

• Using the volume of all the components given by the 3D CAD software (taking into account the obelisk mirror holder of the green laser injection mirror) and
• using the density of (dry) air,

The bouyancy force is ~ 62 grams. Using the spring constant measured by the Type B team of 1.499 kg/mm (for 3 blades in parallel), the displacement in vacuum is expected to be 41 µm down, which is negligible for our purposes.