uncertainty associated with the generated force (and the laboratory’s claimed CMC) is calculated, as for
national force standard machines, from the uncertainties associated with these measurements, together with
the other contributions detailed in section 4. It is necessary also to perform comparisons between the force
calibration machine and an appropriate national force standard machine using high quality transfer
standards – the procedure for this work may be as described in section 5.2 but the results need to be
analysed in a different way, as it is a comparison exercise rather than a calibration. The analysis needs to
demonstrate whether or not the results from the two machines are metrologically compatible – one method
for assessing this is described in [4] and involves determining whether or not the En values calculated across
the range of applied force exceed unity. If these values do exceed unity, it is not sufficient simply to increase
the CMC to reduce the En value to an acceptable level, but the whole uncertainty budget associated with the
force calibration machine (and with the comparison procedure) should be reviewed to the satisfaction of the
national accreditation body.