Difference between bar and barg

The 'g' added on to bar means 'gauge', as opposed to bara, meaning 'absolute'.

The 'zero' of a normal gauge is normally set at atmospheric pressure (things like tire pressure gauges, water gauges etc.) These gauges will read as "10 bar" but really mean that the absolute pressure is 10 bar + atmospheric pressure (~1.01325 bar).

Some gauges however are absolute gauges. These might include weather gauges, or gauges on closed processes.

bara = barg + atmospheric pressure