Usually there is no differences between tle L and R needles.The duct pressure change with thrust change,but it doesn't affect the pressurization.The system is automatic,and it's no use to check this indicator except on engine start.
"Differences between L and R duct pressure on the bleed air duct pressure indicator are considered normal as long as there is sufficient air for cabin pressurization" OM 2.
So ,just check the cabin altimeter/differential pressure indicator,if you feel something is wrong.
No other specification on the technical man.
Al
