UNIT WORKS GOOD, AND SOMEONE ADDED A 12 VOLT LIGHT AND THE METER LIGHTS UP NICE AND WHITE BACKGROUND. THAT'S WHAT THAT LITTLE TOGGLE SWITCH IS ABOUT ON THE REAR, (UP LIGHT IS ON) ( DOWN IT TURNS IT OFF) BEST OF BOTH WORLDS UNIT IS CLEAN INSIDE AND OUT. COMES WITH COPY OF THE OPERATING MANUAL. SHELF BX