California Code, Food and Agricultural Code (Formerly Agricultural Code) - FAC § 35783.1

A recording thermometer shall be installed in each dairy farm milk storage tank used to cool or store market milk during the milking process. If a farm pickup tanker is used in lieu of a dairy farm tank, the recording thermometer shall be installed in the pipeline following an effective cooling device that cools the milk to 45 degrees Fahrenheit (7 degrees Celsius) or less. Nothing in this section shall be construed as meaning that a recording thermometer must be attached when milk tankers are moved over the road. The secretary shall issue regulations providing standards for these thermometers including installation and operation.