On the concentrated contact as a viscometer

Lubricant viscosities from published concentrated contact-based measurement s are compared with measurements by conventional viscometry for overlapping pressures and viscosities. Contrary to published claims there are importan t differences. The greater than exponential pressure-viscosity behaviour, w hich is known to occur at high pressures, is absent from contact measuremen ts. Deficiencies in contact-based techniques are probably due to assumed co nstitutive behaviour and are not related to time scale. In general, contact -based methods are poorly conditioned for the measurement of pressure-visco sity coefficients.