Until the 1980s, gasoline station dispensers were generally equipped with mechanical computers that measured the amount of fuel flowing through to motorists’ tanks. A gear system, inside a meter, was connected to a series of wheels. Each wheel, 4 inches or so in diameter and about an inch thick, had numbers embossed on its outer perimeter. 

As gasoline flowed through the meter, the wheels turned and displayed their numbers through small apertures in the face of the pump. Some wheels displayed the number of gallons dispensed. Other wheels displayed the dollar amount of the transaction.

Today, most service station dispensers rely on electronic gallonage and price displays. However, many pumps with mechanical meters are still in operation. The wheels in these pumps, that display gallonage and price, are referred to as computer wheels.