“…The third type of flow standard, calibrated bellows [12,15,16,22], also has no sliding seal, and it eliminates the complications due to the oil by driving the bellows directly. Its chief disadvantage is that the bellows volume V(x) must be calibrated as a function of its linear displacement x. Jousten et al [12] found that V(x) was more linear for a formed bellows than for a welded diaphragm bellows, although Gronych et al [22] later were able to use a welded diaphragm bellows despite its nonlinearity.…”