ebay seller said:The 52mm Smoked Face Digital Dual Combination Boost / Volt Gauge (PSI) gives the benefit of having two gauges in one and with the ignition switched off the gauge face is totally black. When the ignition is switched on the gauge comes to life and does a 15 second system voltage check displaying the result on the blue digital display. After 15 seconds the gauge automatically switches over to Boost Mode and displays the present boost pressure in the blue digital display which is surrounded by an attractive LED boost level indication display.