A system useful for monitoring or controlling the back pressure of fluid in a wellbore is disclosed. The system may include: a choke assembly including: a housing having an inlet, an outlet, and a bore; a choke member disposed in the bore for controlling a flow of a fluid from the inlet to the outlet, and a rod coupled to the choke member and extending through the housing; a cylinder including: a housing having an axial bore; a piston, directly or indirectly coupled to the rod, disposed in the axial bore and separating the axial bore into a first chamber and a second chamber; a position indicating device fluidly coupled to the second chamber, wherein a change in volume of fluid in the second chamber causes a corresponding change in volume of fluid in the position indicating device, thereby indicating a change in the position of the choke member.