California Code, Health and Safety Code - HSC § 114159

(a) Except for vending machines, an accurate, easily readable, metal probe thermometer suitable for measuring the temperature of food shall be readily available on the premises of each food facility holding potentially hazardous food.

(b) A food temperature measuring device with a suitable small-diameter probe that is designed to measure the temperature of thin masses shall be provided and readily accessible to accurately measure the temperature in thin foods such as meat patties and fish fillets.

(c) Food temperature measuring devices that are scaled only in Fahrenheit shall be accurate to ±2°F in the intended range of use.Food temperature measuring devices that are scaled only in Celsius or dually scaled in Celsius and Fahrenheit shall be accurate to ±1°C in the intended range of use.

(d) Food temperature measuring devices shall not have sensors or stems constructed of glass, except that thermometers with glass sensors or stems that are encased in a shatterproof coating, such as candy thermometers, may be used.

(e) Food temperature measuring devices shall be calibrated in accordance with manufacturer's specifications as necessary to ensure their accuracy.