Auto Meter 5401 Pro-Comp Liquid-Filled Mechanical Vacuum/Boost Gauge Traditional incandescent lighting illuminates around the perimeter of the dial Liquid dampened movement provides smooth pointer movement and extended service life in harsh environment applications. Liquid filled design for superior resistance to shock, vibration, and the elements. Auto Meters race proven mechanical instruments provide trusted accuracy while being simple to install No electrical system required for gauge operation - compatible with every street or race vehicle