Steam turbine installation on passenger ship. American terms 1918:
A, safety valve on primary stage. B, engaging latch to safety stop on governor. C, governor regulator. D, ball weights on governor. E, chain fall and gear for lifting top half of casing. F, governor. G, connecting rods to revolution
Those are the turbines ( turbine casings ) not the boilers . The pressure gauges on the top show the pressure at each stage of the turbine .
That should help answere Marconi Sahibs question too .
The pressure drop between stages is a function of the turbine design and is not adjustable by the engineers on watch . However if there is a problem with a row of turbine blades ( either on the rotor or the fixed blades on the casing ); or a problem with the seals beween stages then this would show up and be detected by observation of the recorded pressures taken from the gauges you have remarked upon on the casing top.
The pressure gauges on the turbine front would be gland steam pressure on the forward and aft shaft seals .
I hear you mate - boring times and I couldn't stand the white gloves! I only did enough time for my ticket, never went back - mind you they converted all out steam ships in to motor ships or scraped em!