California Code, Business and Professions Code - BPC § 13489

(a) The device mechanism accurately measures the quantities of the gasoline being simultaneously withdrawn from each of the two tanks and the quantity dispensed.

(b) The device mechanism accurately and visibly records and displays the resulting combined quality, the total quantity, the price per gallon or liter for the particular quality combination being dispensed, and the total price of the quantity of gasoline dispensed at the particular sale.

(c) The device has a locking selector mechanism which prevents the changing of the proportion of the two qualities being combined during the dispensing of the desired quantity.

The provisions of this section shall not supersede any other provisions in this chapter, except that they shall supersede the provisions of Sections 13442, 13443, 13480, 13483, 13486, 13487, and13488to the extent necessary to authorize the operation of a blending type of pump connected to two tanks containing two different products, or two different grades of the same product, which, when blended together in different proportions, will produce gasolines of different octane rating, each blend of which shall meet the specifications for gasoline as required by this chapter.