  Atomic force microscope (AFM) users often calibrate the spring constants of
cantilevers using functionality built into individual instruments. This is
performed without reference to a global standard, which hinders robust
comparison of force measurements reported by different laboratories. In this
article, we describe a virtual instrument (an internet-based initiative)
whereby users from all laboratories can instantly and quantitatively compare
their calibration measurements to those of others - standardising AFM force
measurements - and simultaneously enabling non-invasive calibration of AFM
cantilevers of any geometry. This global calibration initiative requires no
additional instrumentation or data processing on the part of the user. It
utilises a single website where users upload currently available data. A
proof-of-principle demonstration of this initiative is presented using measured
data from five independent laboratories across three countries, which also
allows for an assessment of current calibration.
