What will be pressure of gas measured by manometer if mercury starts to rise on the other side?
The $P_a$ side is open to the gas container and the $P_0$ side is open to the atmosphere with atmospheric pressure $P_0$.
The pressure of gas $P$ here is $P_0 + \rho g H$ where $H$ is as given in image and other symbols have usual meanings.
Now here is my question,
What would be the pressure of a gas if the pressure of gas was high enough to cause the liquid (mercury here) to move down the U shaped tube and rise up on the other side?