California Code, Business and Professions Code - BPC § 13490

(a) The device mechanism accurately measures the quantities being simultaneously withdrawn for dispensing as a combined product from each of the two tanks when the combined product is dispensed, the quantity being dispensed from the gasoline tank when gasoline alone is dispensed, or the quantity being dispensed from the tank containing a premixture of gasoline and motor oil when the premixture alone is dispensed.

(b) The device mechanism accurately and visibly records and displays: (1) the ratio of gasoline to motor oil or premixture, the quantity of each ingredient being dispensed, the price per gallon or liter for the gasoline being dispensed, and the price per quart or liter for any motor oil or premixture being dispensed or (2) the ratio of gasoline to motor oil or premixture and the price per gallon or liter for the product being dispensed.

(c) The device mechanism prevents the changing of the ratio of gasoline to motor oil or premixture during dispensing.

The provisions of this section shall supersede Sections 13442, 13443, 13480, 13483, 13486, 13487, and13488to the extent necessary to authorize the operation of the above-described blending type of pump connected to two tanks, one containing motor oil, or a premixture of motor oil and gasoline in a known ratio, and the other gasoline, provided that the motor oil shall in its separate state meet the specifications for motor oil as required by Section 13460 and that the gasoline shall in its separate state meet the specifications for gasoline as required by Section 13440.