Originally Posted by krenshaw
do you know when it is finished carbonating by a certain psi number on the gauge? or is that just to be sure you don't lose any of the pressure to oxidize the beer in the process of the couple weeks of naturally carbonating?
When the pressure stops rising, it means your yeast is done eating the priming sugar. At room temperature, for an average CO2 volume, the pressure is around 25psi.
While priming, this tool is useful for the both reason you highlighted: to know when the beer is carbonated, and to make sure you do not have a slow leak somewhere.
It can also be used to ferment under pressure, and to transfer beer under pressure.