Barb Fitting Regulator Cap

What is the barb fitting in the regulator cap used for?  How and where should it be connected if I choose to use it, and what should I do with it if I don’t?

Aeromotive EFI bypass regulators support 1:1 vacuum/boost referencing. Connect a vacuum/boost line between the intake manifold and regulator cap for port fuel-injected engines. Set base pressure with the line disconnected. For TBI engines or injectors above the throttle blade, leave the port open to atmosphere.

Note: 1:1 ratio is in PSI. Vacuum gauges measure in "HG, where 2"HG ≈ 1 PSI. For example, 10"HG at idle drops fuel pressure by 5 PSI.

For more details, ask to speak to a Tech.