Primary, transfer and working instruments and systems for pressure det
ermination from the barometric range down to low pressures are examine
d on the basis of the measurement uncertainty level attained at IMGC.
In low-pressure primary measurements over the 10(5)-10(2) Pa range, re
lative uncertainties from +/- 1.5 x 10(-5) to +/- 1 X 10(-2) can be ob
tained. At lower pressures a relative uncertainty of a few parts in 10
(3) is considered satisfactory; it increases to 10(-2) for 10(-5) Pa p
ressures. Calibration results concerning transfer gauges, as well as s
hort- and long-term repeatability of the most widely used working gaug
es are reviewed.