What is "Relative Pressure" on a gas table?

[Remusco]

I came across this problem while studying for my PE exam:

I'm not sure what "P_r2" is supposed to represent. Obviously 480 psia is not 697.5 times atmospheric pressure.

This is what the table looks like with the "relative pressure" column:

How does "relative pressure" relate to the absolute pressure?

 

[Lnewqban]

Pr should refer to pressure ratio or increased pressure at point 2 respect to point 1.

For steam turbines, Pr is the reduction in the value of the fluid pressure as it expands through the blades in the turbine from inlet to outlet.

The information in the posted table is not related to the Pr in the problem, as we have anything but air at low pressure.

That pre-turbine added heat (Qin) increased both, the temperature and the pressure of that original cave air.

Consider that the problem asks for the 2-3 produced work, which means useful shaft mechanical energy.
Because of that, you will need to consider the given efficiency data.

Remember that turbine efficiency is the ratio of actual work output from the shaft of the turbine to the net input thermal energy.