Subject: How is vacuum affected by atmospheric pressure in a steam condenser

The condenser of a steam turbine is a sealed system so why does the vacuum 
vary with atmospheric pressure if all the other conditions remain the 
same? I have noticed that as atmospheric pressure drops the vacuum in the 
condenser becomes less negative and vice versa. The condenser vacuum is 
measured in barg ie. 1000mbar is read as zero. The atmospheric pressure is 
measured in bar absolute. This is a personal question and will enable me 
to understand my job as a power station engineer better.

Re: How is vacuum affected by atmospheric pressure in a steam condenser