When you need a precise low pressure measurement, a capsule gauge is the instrument to use.
Capsule gauges are used almost exclusively for measuring gaseous media.
These gauges are very precise with pressures that range lower than what the bourdon tube gauge can read.
They are often employed in low pressure pneumatic systems, breather valves, overpressure monitoring, filter monitoring and vacuum pumps, as well as many other situations where precision is a necessity.