This article applies to farm milk tanks, as defined, only when these are used, or are to be used, under an express contract between the producer and the purchaser and on the premises of the producer, for the commercial measurement of milk or other fluid dairy products. If such measurement is accomplished by the means of a fluid meter, this paragraph does not apply; in such case, the meter shall be subject to approval by the commissioner and to the applicable provisions of the article for liquid measuring device.