Autometer Stack 52mm -30INHG to +30 PSI (Incl T-Fitting) Mechanical Boost Pressure Gauge - WhiteMechanical gauges do not require 12V power to operate. They make direct physical contact with the item they are reading. They do this through tubing or lines, which eliminates the need for electric signals. Installation Instructions Mechanical gauges do not require 12V power to operate. They make direct physical contact with the item they are reading. They do this through tubing or lines, which eliminates the need for electric signals. Ideal for